Bone mineral density (BMD) of the lumbar spine was measured in 97 long-term survivors of childhood cancer 5-23 years after diagnosis using dual-energy X-ray absorptiometry (DXA). They had been treated for acute leukemia (n = 22), brain tumors (n = 16), lymphomas (n = 16), Wilms' tumor (n = 10), neuroblastoma (n = 7) and other cancers (n = 26). The correlations between BMD and the Z-scores for weight for height, height for age and weight for age at diagnosis and follow-up were evaluated with stepwise multiple regression. Correlations with cumulative corticosteroid and radiation dose were examined with Spearman's correlation coefficient. The number of nature of fractures were noted. A BMD Z-score of below -2 was present in 13 and a BMD Z-score of -1 to -2 in 31 children. In total, a low BMD was observed in 45% of children. Height for age at follow-up correlated significantly with BMD Z-score. Increasing doses of cranial irradiation (18-54 Gy) were associated with lower BMD (p = 0.001, Spearman). This was true also for 22 children with acute lymphoblastic leukemia (ALL) who had received 18-24 Gy cranial irradiation (p = 0.04, Spearman). Fractures occurred in 14 children following trauma. The difference in BMD Z-scores of children with and without fractures did not achieve statistical significance although the majority of the children with fractures had low BMD Z-scores. The significant inverse correlation between height for age at follow-up and BMD must be interpreted with the realization that DXA is not a volumetric measurement of BMD and that short stature is associated with a smaller skeletal mass.