The relationship between cutaneous malignant melanoma (MM) and possible risk factors was assessed in a case-controlled study. Two hundred patients and 200 non-melanoma controls of German origin matched for age and sex were interviewed and examined for pigmented moles and pigmentation characteristics. In patients with MM significantly more melanocytic nevi greater than or equal to 2 mm (MCN) were found (mean, 53 MCN) compared to control cases (mean, 18 MCN). For persons with greater than 60 MCN the relative risk (RR) for developing MM increased 15 times compared to less than or equal to 10 MCN. Additional independent markers for an increased risk were presence of atypical MCN (RR = 7 vs. none) found in 45% of patients and in 5% of the control group, moderate to large numbers of actinic lentigines (RR = 6.2 vs. none), and lack of tanning as well as a tendency to sunburn (skin type I; RR = 2.2 vs skin type IV) No significant correlation was found between the relative risk for MM and hair color, eye color, duration of free time sun exposure and number of sunburns. Individuals with permanent outdoor profession and sun exposure, however, showed a clearly increased relative risk for developing MM.