In the USA, family-based treatment (FBT) with inpatient medical stabilization as needed is the leading evidence-based treatment for youth with anorexia nervosa (AN). In continental Europe, typically inpatient multimodal treatment targeting weight recovery followed by outpatient care (IMT) is standard care, if prior outpatient treatment was not sufficient. Our aim was to compare weekly weight gain and hospital days over six months for adolescents receiving FBT (USA) versus IMT (Germany) using naturalistic treatment data. To yield similar subgroups of youth aged 12-18 years, inclusion criteria were a percent median BMI (%mBMI) between 70-85 and the restrictive AN subtype. Weight gain and hospital days were compared, adjusted further in a multiple linear regression analysis (MLRA) for baseline group differences. Samples differed on baseline %mBMI (FBT [ = 71], 90.5 ± 12.8; IMT [ = 29], 78.3 ± 9.1, < 0.05). In subgroups with comparable baseline %mBMI, the weekly weight gain over 6 months was similar (FBT [ = 21]: 0.35 ± 0.18 kg/week; IMT [ = 20]: 0.30 ± 0.18, = 0.390, = 0.166 after MLRA), but achieved fewer hospital days in FBT (FBT [ = 7]: 4 ± 6 days, IMT [ = 20]: 121 ± 42 days, < 0.0001 before and after MLRA). FBT may be effective for a subgroup of adolescents with AN currently receiving IMT, but head-to-head studies in the same healthcare system are needed.