BACKGROUND: Craniopharyngiomas are tumorous embryogenic malformations. As the survival rate after craniopharyngioma is high (92 %), prognosis and quality of life (QoL) in survivors mainly depend on adverse late effects such as obesity. PATIENTS AND METHODS: We analyzed 214 children and adolescents with craniopharyngioma. The records of 185 patients (86 %) were available for retrospective analysis of weight profiles and risk factors for obesity. Quality of life (QoL) was measured in 145 patients by the Fertigkeitenskala Münster/Heidelberg score (FMH) and in 77 patients by PEDQOL questionnaire. RESULTS: Eighty-two of 185 patients (44 %) developed severe obesity (body mass index [BMI] > 3 SD). Obese patients were compared with 79 patients (43 %) who kept normal weight (BMI < 2 SD). No differences between obese and normal weight patients were found in terms of gender distribution, age at diagnosis and follow-up period. However, the BMI SDS at the time of diagnosis was higher (p < 0.0001) in patients who developed obesity than in those who did not. Furthermore, obese patients presented with bigger tumors (p < 0.05) and a higher rate of a hydrocephalus requiring a shunt (p < 0.05) and hypothalamic involvement (p < 0.05). The mothers of patients who developed severe obesity had a higher BMI (p < 0.001) at the time of diagnosis. Obese patients had a higher height-SDS at diagnosis (p < 0.05) and at the time of last follow-up (p < 0.05) when compared with normal weight patients. A prediction model for severe obesity after craniopharyngioma was calculated by logistic regression based on the risk factors: patient's BMI > 2 SD at diagnosis (p < 0.05; odds ratio: 16.4), hypothalamic involvement (p < 0.05; odds ratio: 3.4) and maternal BMI > 25 kg/m(2) (p < 0.05; odds ratio: 4.6). Significant increases in BMI (p < 0.001) occurred during the early post-operative period especially during the first three years after diagnosis. FMH percentiles correlated negatively with BMI SDS (Spearman r: - 0.37; p < 0.001). Children with craniopharyngioma rated their QoL more negative (p < 0.05) in regard to physical abilities, cognitive functioning and social functioning when compared with healthy children of the same age group. Severely obese patients with craniopharyngioma estimated their QoL lower (p < 0.05) for all domains except for autonomy, cognition and familial integration in comparison with non-obese patients. CONCLUSION: Hypothalamic tumor involvement and familial disposition for obesity are risk factors for the development of severe obesity in patients with craniopharyngioma. As weight gain starts early after diagnosis and severe obesity causes a reduction in QoL, early therapeutic efforts should be considered in patients at risk. To confirm our results the prospective multicenter study Kraniopharyngeom 2000 on children and adolescents with craniopharyngioma was initiated (www.kraniopharyngeom.com).