The "aplastic crisis" of congenital spherocytic anemia is a well-documented syndrome.1,2It is known that these erythroblastopenic states may occur in several members of a family within a short period of time. Recently these crises have been also described in sickle-cell anemia.3,4The purpose of this article is to report on members of two families with sickle-cell anemia in which aplastic crises developed within a short period of time. Report of Cases Family A Case1A.—This 5-year-old Negro boy was admitted to the hospital on Nov. 28, 1955. He had been known to have sickle-cell anemia since the age of 5 months. In November and December, 1954, he had had two attacks of cerebral thrombosis leaving him with aphasia and inability to properly handle his oral secretion and a paresis of his left upper extremity. One day prior to admission he was noted to be pale and weak.