Event-free survival of children and adolescents with ALK-positive anaplastic large cell lymphoma (ALCL) reaches 65-75% with current chemotherapy regimen. Risk stratification of children with ALCL was, until now, based on clinical parameters. More recently, pathological and biological risk factors have been described in trials applying BFM-type chemotherapy. Histological subtypes containing small-cell or lymphohistiocytic components indicate a high risk of failure. Minimal disseminated disease (MDD) detected by qualitative RT-PCR for NPM-ALK in bone marrow or blood is associated with a relapse risk of 50%. Quantification of MDD and persistent minimal residual disease (MRD) characterize very high risk patients. Serum ALK-autoantibody titres inversely correlate with relapse risk. The combination of MDD and ALK-antibody titre separates both low and very high risk patients from those with standard risk. In relapse, the time of relapse/progression, central nervous system and bone marrow involvement are major risk factors. In conclusion, MDD, MRD, ALK-antibody titres and histological subtype are strong biological risk factors in childhood ALCL. The combination of MDD and ALK-antibody titre may serve for patient stratification in upcoming clinical trials.