Summary Background  Patients with melanoma are at increased risk of developing a subsequent melanoma. Objectives  To estimate the risks of developing a second primary in situ or invasive cutaneous melanoma after a first melanoma, between 1989 and 2008. Methods  Patients were followed until diagnosis of a second melanoma, date of death or end of study. Cumulative risks, standardized incidence ratio (SIR, observed second melanomas divided by background age‐, calendar‐ and sex‐specific incidence rates of melanoma, as recorded in the Netherlands Cancer Registry) and absolute excess risk (AER, observed minus expected per 10 000 person‐years) of second melanomas were calculated. Results  In total, 10 765 patients with in situ melanoma and 46 700 with invasive melanoma were included. The cumulative risks of a second invasive melanoma after a first in situ or invasive melanoma at 20 years of follow‐up were 6·2% and 5·0%, respectively. The relative risk of developing any melanoma (in situ or invasive) after any first melanoma (measured as SIR) varied from 12·4‐fold invasive after invasive melanoma; 95% confidence interval (CI)  = 11·6–13·2 to 26·4‐fold (in situ after in situ melanoma; 95% CI = 22·6–30·7) increase compared with the general population. SIRs and AERs remained elevated up to 20 years after the first melanoma. Conclusions  This study shows significantly increased long‐term risks (both relative and absolute) of developing a second invasive melanoma after a first melanoma (invasive and in situ), and might serve as a basis for follow‐up guidelines.