The occurrence of a transitory aplasia followed shortly thereafter by an acute leukemia in a known sequence in children is rare. We report 13 observations involving children between 6 months and 10 years of age. Splenomegaly was observed in 5 patients and hepatomegaly in two. There was a tricytopenia in 5 cases, bicytopenia in 4 and an isolated cytopenia in the remaining 4 cases. The phase of aplasia was short, lasting from 6 to 30 days. Complete bone marrow recovery occurred with integral restitution. Remission was spontaneous or followed transfusion or corticosteroid therapy and lasted for 2 to 6 months. The leukemia had no particular character when it appeared: there was one acute myeloblastic leukemia, 11 acute lymphoblastic cases and one sarcoma. Median survival time was 5 to 32 months and relapses were not aplasic. It is noteworthy that among these cases there are two long remissions lasting more than ten years. The interpretation of these observations is difficult because of the following choice: an initially non-leukemic aplasia or a leukemia present at the onset but undetected, camouflaged or confined to several infrequent blast cell islets.