The emergence of non-Hodgkin lymphoma (NHL) during childhood and adolescence as a secondary neoplasm (SN) after previous cancer other than NHL is rare. To describe the characteristics and outcome of NHL following previous cancer other than NHL in children and adolescents, this study analysed the data of patients reported to the NHL-Berlin-Frankfurt-Münster study centre from 1986 to 2005. Out of the total of 2968 NHL-patients registered, 11 patients were assessed as having suffered from NHL as a proven SN. Four additional children had most likely suffered from NHL as an SN, but a late relapse of the first neoplasm could not be ruled out unequivocally. In the patients with proven SN, median age at diagnosis of the primary malignancy was 3·9 years (range 2–11·7). The median age at diagnosis of NHL was 7·6 years (range 4·7–18). Only lymphoblastic (n = 7) and diffuse large B-cell (n = 4) lymphomas were diagnosed as SN. The estimated 5-year event-free survival from time of diagnosis of NHL was 91% [95% confidence interval (CI) 74–100%] in patients with proven SNs and 84% (95% CI 63–100%) when the patients with probable SNs were included in the analysis. We concluded that secondary NHL in children and adolescents confers a favourable prognosis.