Background:Our previous studies revealed cyclicity in the incidence rate of skin malignant melanoma(SMM;ICD9,Dx:172)in the Czech Republic(period T=7.50～7.63 years),UK(T=11.00 years)and Bulgaria(T=12.20 years).Incidences com- pared with the sunspot index Rz(lag-period dT=+2,+4,+6,+10 or+12 years)have indicated that maximal rates are most likely to appear on descending slopes of the 11-year solar cycle,i.e.,out of phase.We summarized and explored more deeply these cyclic variations and discussed their possible associations with heliogeophysical activity(HGA)components exhibiting similar cyclicity. Methods:Annual incidences of SMM from 5 countries(Czech Republic,UK,Bulgaria,USA and Canada)over various time spans during the years 1964～1992 were analyzed and their correlations with cyclic Rz(sunspot number)and aa(planetary geomagnetic activity)indices were summarized.Periodogram regression analysis with trigonometric approximation and phase-correlation analysis were applied.Results:Previous findings on SMM for the Czech Republic,UK and Bulgaria have been validated,and cyclic patterns have been revealed for USA(T=8.63 years,P<0.05)and Canada(Ontario,T=9.91 years,P<0.10).Also,various ’hypercycles’were established(T=45.5,42.0,48.25,34.5 and 26.5 years,respectively)describing long-term cyclic incidence patterns.The association of SMM for USA and Canada with Rz(dT=+6 and+7 years,respectively)and aa(dT=?10 and+9 years,respectively)was described.Possible interactions of cyclic non-photic influences(UV irradiation,Schumann resonance signal,low-frequency geomagnetic fluctuations)with brain waves absorbance,neuronal calcium dynamics,neuro-endocrine axis modulation,melatonin/serotonin disbalance and skin neuro-immunity impairment as likely causal pathways in melanoma ap- pearance,were also discussed.Conclusion:The above findings on cyclicity and temporal association of SMM with cyclic envi- ronmental factors could not only allow for better forecasting models but also lead to a better understanding of melanoma aetiology. Background: Our previous studies found cyclicity in the incidence rate of skin malignant melanoma (SMM; ICD9, Dx: 172) in the Czech Republic (period T = 7.50-7.63 years), UK (T = 11.00 years) and Bulgaria 12.20 years) .Incidences com- pared with the sunspot index Rz (lag-period dT = + 2, + 4, + 6, + 10 or + 12 years) have indicated that maximal rates are most likely to appear on descending slopes of the We summarized and explored more deeply these cyclic variations and discussed their possible associations with heliogeophysical activity (HGA) components exhibiting similar cyclicity. Methods: Annual incidences of SMM from 5 countries (Czech Republic, UK, Bulgaria, USA and Canada) over various time spans during the years 1964-1992 were analyzed and their correlations with cyclic Rz (sunspot number) and aa (planetary geomagnetic activity) indices were summarized. Periodogram regression analysis with trigonometric approximation and phase- correlation analysis were applied. Results: Prev ious findings on SMM for the Czech Republic, UK and Bulgaria have been validated, and cyclic patterns have been revealed for USA (T = 8.63 years, P <0.05) and Canada (Ontario, T = 9.91 years, P <0.10) describing long-term cyclic incidence patterns. The association of SMM for USA and Canada with Rz (dT = + 6 and + 7 years (T = 45.5,42.0,48.25,34.5 and 26.5 years, respectively) , respectively) and aa (dT =? 10 and + 9 years, respectively) were described. Povements of cyclic non-photic influences (UV irradiation, Schumann resonance signal, low-frequency geomagnetic fluctuations) with brain waves absorbance, neuronal calcium dynamics , neuro-endocrine axis modulation, melatonin / serotonin disbalance and skin neuro-immunity impairment as likely causal pathways in melanoma ap- pearance, were also discussed. Conlusion: The above findings on cyclicity and temporal association of SMM with cyclic envi- ronmental factors not only allow for better forecasting models but also lead to a better understanding of melanoma aetiology.