Male patients with Bloch-Sulzberger incontinentia pigmenti (IP type II) are rare and more severely affected than their female counterparts, with a significant occurrence of sex chromosome aneuploidy. This document introduces a new male IP type II patient and reviews 48 males reported with IP. Twenty-eight of the 49 patients meet current criteria for diagnosis of IP type II. The phenotype is variable and the incidence of documented developmental delay is 25%. Five patients had Klinefelter syndrome (47,XXY). Most patients were reported prior to 1961 when chromosome analysis was not available. Biopsy and laboratory reports considered to be "consistent with" the diagnosis of IP were seen in patients meeting criteria as well as those who would not currently be given the diagnosis. The histologic findings considered diagnostic are varied. This variability may be accounted for by differences in stage of disease, biopsy site, histologic technique, and reporting style. Conversely, this may indicate that the diagnostic weight given to the biopsy should be reconsidered. Eosinophilia was not a consistent finding. Overall, differences in reporting, ascertainment, and length of follow-up lead to difficulty in interpreting or predicting the natural history of males with IP type II. Based on the existing literature, they appear to have a higher rate of mental retardation than the general population, but there does not appear to be a correlation between severity of physical and mental involvement. The presence of sex chromosome aneuploidy documented in the more recent cases emphasizes the need for chromosome analysis in any male patient suspected of IP type II.