Apart from being awake at the onset of their terminal events, the demographic and pathologic profiles of these cases were similar to those of sudden infant death syndrome (SIDS). Altered responses to severe hypotension, bradycardia, and apnea perhaps elicited by aspiration and mediated by cerebellar and vestibular structures may be involved in the pathogenesis of these deaths. A genetic disorder with inheritance being either X-linked or dominant with incomplete penetrance cannot be excluded in the family of one of the infants. A comprehensive review of medical history, an investigation of the circumstances of the death, a thorough postmortem examination with ancillary studies, and preservation of tissues that may be used for gene testing are crucial in explaining these deaths. Attention should be given to the awake or sleep state immediately prior to the sudden clinical collapse and death of infants. Two of the cases, which occurred between 1991 and 2005 were found in a retrospective search of the SIDS database produced by the San Diego SIDS/SUDC Research Project. Three additional cases were identified from the consultation files of one of the authors. 2 tables and 36 references