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.