Objectives: Investigate trends over time and predictors of malignancies among children and young people with HIV. Design: Pooled data from 17 cohorts in 15 countries across Europe and Thailand. Methods: Individuals diagnosed with HIV and presenting to paediatric care less than 18 years of age were included. Time at risk began at birth for children with documented vertically acquired HIV, and from first HIV-care visit for others. Children were followed until death, loss-to-follow-up, or last visit in paediatric or adult care (where data after transfer to adult care were available). Rates of reported malignancies were calculated overall and for AIDS-defining malignancies (ADM) and non-AIDS-defining malignancies (NADM) separately. Risk factors for any malignancy were explored using Poisson regression, and for mortality following a malignancy diagnosis using Cox regression. Results: Among 9632 individuals included, 140 (1.5%) were ever diagnosed with a malignancy, of which 112 (80%) were ADM. Overall, the rate of any malignancy was 1.18 per 1000 person-years; the rate of ADM decreased over time whereas the rate of NADM increased. Male sex, being from a European cohort, vertically acquired HIV, current severe immunosuppression, current viral load greater than 400 copies/ml, older age, and, for those not on treatment, earlier calendar year, were risk factors for a malignancy diagnosis. Fifty-eight (41%) individuals with a malignancy died, a median 2.4 months (IQR 0.6-8.8) after malignancy diagnosis. Conclusion: The rate of ADM has declined since widespread availability of combination ART, although of NADM, there was a small increase. Mortality following a malignancy was high, warranting further investigation.