Objectives: To examine the range of clinical phenotypes, tumour associations, relevant investigations, response to therapy and outcome in a large series of no n selected patients with paraneoplastic neurological disease (PND) affecting th e central nervous system (CNS) in the United Kingdom. Methods: Data were obtaine d on patients either through direct referral or through the British Neurological Surveillance Unit (BNSU) from February 2000 to January 2001. Physicians were a sked to supply information about age and sex of patients, presenting neurologica l syndromes, the basis of the diagnosis of PND, any associated malignancy, and t reatment. Case notes were reviewed and follow up data obtained where possible on e year after notification. Results: A total of 63 patients (48 females, 15 males ) were identified, 48 through the BNSU and 15 through direct referral. Of these 52 were diagnosed as having definite PND, 10 probable PND, and 1 possible PND. T he median age of onset of PND was 66 years (range 30 80 years) and only 7 patie nts (11%) were less than 50 years at presentation. In 53 patients (84%) the PN D preceded the diagnosis of cancer. Paraneoplastic sensory neuronopathy, paraneo plastic encephalomyelitis, and paraneoplastic cerebellar degeneration (PCD) were the most common syndromes reported. The benefit of magnetic resonance imaging i n the diagnosis of the disease was limited, while fluorodeoxyglucose positron em ission tomography was shown to be useful for the detection of an occult malignan cy in 10 out of 14 patients. Antineuronal antibodies were positive in 44/57 (77 %) of cases. The following tumours were diagnosed: small cell lung cancer (30% ), breast cancer (14%), ovarian cancer (8%), non small cell lung cancer (8%) , Hodgkins lymphoma (6%), other (16%). With the exception of PCD associated with mesothelioma all other tumours diagnosed in these patients had been previou sly documented as being associated with PND. Only treatment of the tumour was fo und to be associated with a stable or improved neurological outcome at last foll ow up (Fishers exact test = 4.7, p < 0.03). Median survival time was 43 months (95%CI 28 to 57) from onset of neurological disease as calculated using the Ka plan Meier survival analysis. Conclusions: PND has a striking female prepondera nce usually affecting patients in their sixth decade and above. The median survi val in our study was 43 months. The majority of patients with PND are not known to have cancer at the time of diagnosis. Our study confirms the importance of di agnosing and treating the underlying tumour. Objectives: To examine the range of clinical phenotypes, tumor associations, relevant investigations, response to therapy and outcome in a large series of no n selected patients with paraneoplastic neurological disease (PND) affecting th e central nervous system (CNS) in the United Kingdom . Methods: Data were obtaine d on patients either through direct referral or through the British Neurological Surveillance Unit (BNSU) from February 2000 to January 2001. Physicians were a sked to supply information about age and sex of patients, presenting neurologica l syndromes, the basis of the diagnosis of PND, any associated malignancy, and reatment. Case notes were reviewed and follow up data obtained where possible on e year after notification. Results: A total of 63 patients (48 females, 15 males) were identified, 48 Through the BNSU and 15 through direct referral. Of these 52 were diagnosed with definite PND, 10 probable PND, and 1 possible PND. T he median age of onset of PND was 6 In 53 patients (84%) the PN D preceded the diagnosis of cancer. Paraneoplastic sensory neuronopathy, paraneo plastic encephalomyelitis, and The benefit of magnetic resonance imaging in the diagnosis of the disease was limited, while fluorodeoxyglucose positron em ission tomography was shown to be useful for the detection of an occult malignan cy in 10 out of 14 patients. Antineuronal antibodies were positive in 44/57 (77%) of cases. The following toms were diagnosed: small cell lung cancer (30%), breast cancer (14%), ovarian cancer cell lung cancer (8%), Hodgkin’s lymphoma (6%), other (16%). With the exception of PCD associated with mesothelioma all other tumors diagnosed in these patients had been previou sly documented as being associated with PND. Only treatment of the tumour wa sfo und to be associated with a stable or improved neurological outcome at last foll ow up (Fisher’s exact test = 4.7, p <0.03). Median survival time was 43 months (95% CI 28 to 57) from onset of neurological disease The calculated using the Ka plan Meier survival analysis. Conclusions: PND has a striking female prepondera nce usually affecting patients in their sixth decade and above. The median survi val in our study was 43 months. The majority of patients with PND are not known to have cancer at the time of diagnosis. Our study confirms the importance of di agnosing and treating the underlying tumor.