We report a stillborn female infant with multiple internal and external anatomic abnormalities and mosaicism for isochromosome 12p. These abnormalities included webbed neck, low-set ears, lower jaw tooth bud, left simian crease, shield chest, focal aplasia cutis, diaphragmatic hernia, hypoplastic lungs, agenesis of pericardium, and Meckel's diverticulum. Karyotypic analysis on cord blood lymphocytes showed 10% mosaicism of 46,XX/47,XX, + i(12p), and analysis of skin fibroblasts showed 50% mosaicism for the same karyotype. The parental karyotypes were normal. There are many reported cases describing the anomalies seen in isochromosome 12p. None of these cases, however, have displayed pericardial agenesis or aplasia cutis. The clinical and cytogenetic features of Pallister-Killian syndrome are reviewed.