Three cases of busulfan-associated convulsions in 28 bone marrow transplant recipients are reported. Convulsions occurred in spite of anticonvulsant prophylaxis in two of the three cases. Fits were generalized; no neurological deficit was found after the episodes and there were no recurrences. Although conditioning regimens including busulfan are used increasingly only rare cases have been reported and little mention of this side effect is made. We emphasize that convulsions are not infrequent side effect of conditioning regimens including high dose busulfan, and efficient anticonvulsant prophylactic regimens should be used.