BACKGROUND: The condition known as macrocephaly-cutis marmorata telangiectatica congenita syndrome (M-CMTC) is a rare congenital syndrome of unknown etiology characterized by macrocephaly and vascular lesions that have been described as either cutis marmorata or cutis marmorata telangiectatica congenita (CMTC). Most patients also exhibit facial and limb asymmetry; somatic overgrowth; developmental delay; capillary malformations of the nose, philtrum, and/or upper lip; neurologic abnormalities; syndactyly or polydactyly; craniofacial abnormalities; and joint laxity or soft skin. OBSERVATIONS: We describe 12 patients with this condition from tertiary care medical centers (8 cases) and accrued via an M-CMTC support group Web site (4 cases). All patients showed reticulated or confluent port-wine stains (PWS), not CMTC. Seven of the 12 patients also had centrofacial capillary malformations. In our comprehensive review of 100 previously reported cases, only 34 were accompanied by photographs that were sufficiently clear to review for diagnostic purposes. None had true CMTC, with most having reticulated PWS or persistent cutis marmorata. CONCLUSIONS: Reticulated or confluent PWS and persistent capillary malformations of the central face, rather than CMTC, are the most characteristic cutaneous vascular anomalies seen in so-called M-CMTC syndrome. The name macrocephaly-capillary malformations (M-CM) more accurately reflects the features of this syndrome.