Melatonin (MLT) is directly or indirectly related to cell growth (both of normal and neoplastic cells), to the immune system stimulation and to the endocrine system modulation. This controlled study was carried out to evaluate urinary excretion of MLT in patients suffering from urogenital tract disorders. Eighty-one patients affected by urogenital disorders were divided in two groups (neoplastic and non-neoplastic) and urinary excretion of MLT was evaluated. Mean diurnal (from 8 a.m. to p.m.) urinary excretion of MLT was 4.97 + 6.08 pg/12 h in non-oncologic patients and 4.82 + 6.21 pg/12 h in oncologic patients (p = 0.50). Mean nocturnal (from 8 p.m. at 8 a.m.) urinary excretion of MLT was 11.97 + 9.34 pg/12 h in non-oncologic patients while in oncologic patients it was 7.86 + 8.95 pg/12 h. Statistically significant variation in nocturnal urinary excretion of melatonin was observed in oncologic patients (p = 0.022) versus non oncologic patients.