Several ecological studies have suggested a link between domestic radon concentration and risk of leukemia at all ages. Children with acute lymphoblastic leukemia (ALL) aged 2–14 years were selected from the Hematology‐Oncology Clinic, Children's Hospital, Ain Shams University, Cairo. Full clinical history, complete blood picture, bone marrow aspiration, and radiographic examinations were taken. Due to the sequential study design, indoor radon measurements could only be done for 10% of the 500 ALL patients initially contacted, while 110 controls have agreed to participate in this study. Radon detectors were placed in homes of subjects resided in Cairo since their birth. Radon concentrations were measured within the period from September 1996 to August 1998 by passive alpha‐track radon detectors. Mean indoor radon concentration was higher for case subjects than for control subjects (p < 0.001). The mean alpha dose for case subjects (3.75 mSv.y‐1) was higher than the natural radiation dose value. For categories less than 40, 40–60, 60–90, and 90 or more Bqm‐3of radon exposure, odds ratios (ORs) based on unmatched case‐control analysis were 1.00, 4.64(95% confidence interval (CI) 1.2–18), 7.42(95% CI 2–27.3), and 5.42(95% CI 1.3–21.1) respectively. There was an association between ALL and radon exposure in this study. These data must be regarded as preliminary and further more extensive studies should be done to determine whether the observed association is causal.