The aim of this cross-sectional study was to evaluate the relationship between the condition of bone mineral density and body composition and the adapted physical activity, the number of past fractures and selected somatic characteristics of girls with myelomeningocele (MMC). The study examined 37 girls with myelomeningocele (MMC) at the age of 11.9 ± 1.8 years. Bone mineral content (BMC) and bone mineral density (BMD) of the forearm were measured by dual-energy X-ray absorptiometry (DXA). Anthropometric measurements were also made and selected anthropological indices were calculated. A percentage of body fat, fat mass (FM in kg) and fat-free body mass (FFM in kg) were calculated, whereas the incidence of fractures of lower and upper limbs was evaluated during interviews. Underestimated BMD characteristic for osteopenia occurred only in physically inactive girls. Low % age-matched was observed in all physically inactive girls, whereas it was less pronounced in physically active girls. Statistically significant positive correlations were found between BMD and: body height, sitting height, body weight, BMI, fat mass and fat-free mass. Regardless of physical activity, significantly higher Z-score values (F = 12.9; p ≤ 0.001) were observed in girls who had not suffered from fractures compared to their peers who reported one or more past fractures in different skeletal locations. Active participation in physical activity of children with MMC may be a factor determining good bone tissue condition. The prevention of fractures in children in wheelchairs can be an important part of maintaining healthy bone tissue and a better quality of life.