Survivors of acute lymphoblastic leukemia (ALL) are at risk of osteoporosis and obesity. We studied bone mineral density (BMD), percent of fat mass (%FM), and activity levels in survivors of ALL treated without radiotherapy. Lumbar and total areal BMD (g/cm2) and %FM were measured in 28 survivors (aged 5.7-14.7 years) of childhood ALL by dual-energy X-ray absorptiometry (DXA) scan (GE Lunar, Prodigy) an average of 5 years after completion of chemotherapy (UK Medical Research Council randomized trial protocol XI [UKALL XI]). One boy fractured his arm during treatment. Apparent volumetric lumbar BMD (BMD vol; g/cm3) was calculated and %FM was adjusted for sex and age (%FM adj). Physical activity was measured by accelerometer and questionnaire. The results were compared with 28 sex- and age-matched healthy controls. Total body and lumbar areal BMD (g/cm2) were not different between the ALL group and the control group. However, mean lumbar BMD vol in survivors of ALL was significantly lower than in controls (0.303 ± 0.036 g/cm3 vs. 0.323 ± 0.03 g/cm3; p < 0.01), which mostly was caused by the difference in boys (0.287 ± 0.032 g/cm3 vs. 0.312 ± 0.027 g/cm3; p < 0.05). Weekly activity score by questionnaire was significantly lower in the ALL group than in the control group (geometric mean 50 vs. geometric mean 74; p < 0.05). Male gender, low activity levels and an intravenous (iv) high dose of methotrexate were associated with low lumbar BMD vol. Patients who received an iv high dose of methotrexate (n = 18) had significantly higher %FM adj than those with intrathecal methotrexate only (n = 10; 141 ± 70% vs. 98 ± 37%; p < 0.05). In conclusion, male survivors of childhood ALL have reduced lumbar BMD vol, whereas no such difference was seen in girls. Overall, survivors of ALL were physically less active than their healthy controls and lower activity correlated with lower lumbar BMD vol and higher %FM adj.