Although children with haemophilia are advised to participate in physical activities, their physical fitness has not been studied in a large group. In addition, children with haemophilia may be at increased risk for becoming overweight as a result of inactivity because of joint bleedings or because of overprotection. This study aimed to assess physical fitness (aerobic capacity), joint status, muscle strength, quality of life (QoL), self-reported motor competence and also prevalence of overweight and its association with physical parameters. Weight and height were measured. Skin folds were measured unilaterally at biceps, triceps, subscapular and supra-iliac sites. Aerobic capacity was determined on a cycle ergometer or with a 6-min walk test (6MWT). Muscle strength and active range of motion of elbows, knees and ankle joints were measured. Self-reported motor competence was measured with the 'Competentie BelevingsSchaal voor Kinderen'. Joint pain was scored on a Visual Analogue Scale. The Haemo-QoL Index was used to measure QoL. In 158 Dutch boys with haemophilia, with a mean age of 12.7 years (SD 2.9), normal aerobic capacity and muscle strength were found. Joint pain was reported by 16% of the participants. The prevalence of overweight (16%) was slightly increased when compared with healthy Dutch boys (13.5%). Being overweight had a negative association with the6MWT and QoL. Dutch children with haemophilia have normal aerobic exercise capacity and muscle strength. The majority also has normal joint mobility. Prevalence of overweight is slightly increased.