Multiple measurements of nocturnal penile tumescence and rigidity (NPTR) are widely accepted as a method to differentiate psychogenic erectile dysfunction (ED) from organic ED.However,direct evidence remains limited regarding the first-night effect on NPTR measurement using the RigiScan.Here,we evaluated the first-night effect on the results of NPTR measurement to validate the necessity of NPTR measurement for two consecutive nights,particularly when abnormal first-night measurements are recorded in a laboratory setting.We retrospectively reviewed 105 patients with a complaint of ED,who underwent NPTR measurement using the RigiScan in the Department of Infertility and Sexual Medicine,the Third Affiliated Hospital of Sun Yat-sen University (Guangzhou,China),for two consecutive nights,during the period from November 2015 to May 2016.NPTR parameters were collected and analyzed.We found that more effective nocturnal erections were detected during the second night than during the first night (P ＜ 0.001).Twenty percent of all patients had no effective erection during the first night,but exhibited at least one effective erection during the second night.The negative predictive value of NPTR measurement during the first night was 43.2％;this was significantly lower than that on the second night (84.2％;P =0.003).Most NPTR parameters were better on the second night than on the first night.The first-night effect might be greater among patients younger than 40 years of age.In conclusion,two consecutive nightly measurements of NPTR can avoid a false-abnormal result caused by the first-night effect;moreover,these measurements more accurately reflect erectile capacity,especially when the first-night record is abnormal in a laboratory setting.