During a 2-year prospective study of 28 leukemic children (24, acute lymphocytic leukemia [ALL]; 4, non-ALL) unselected for musculoskeletal symptoms, objective joint findings were present in 14 cases (p = 0.001 vs normal controls). These findings varied in severity, were most frequently present in the knee (12 of 14 children), and were found most frequently only at disease onset (7 of 14). The group with joint abnormalities had a higher frequency of functionally significant joint complaints prior to diagnosis of leukemia (p = less than 0.01) and radiographic abnormalities of periarticular bone of the knees and ankles (p = less than 0.10). Four of the 5 children with ALL who died had joint findings, a trend whose significance is uncertain because of unequal followup periods.