Isotretinoin (13-cis-retinoic acid), an anti-acne medication, has been found to cause severe birth defects which affect the craniofacial elements, ear, heart, thymus, and central nervous system. Many of these structures receive contributions from the cranial neural crest. Here, we examine the possibility that these teratogenic effects are due to disturbances in neural crest development. Cranial and trunk neural crest explant cultures were exposed to different concentrations of isotretinoin and the cell morphology was monitored at daily intervals. Treated neural crest cells often became rounded or spindle shaped, separated from their neighbors, and frequently detached from the substrate or clumped together. In contrast, neural tube cells and cardiac fibroblasts were relatively unaffected by the drug. These results suggest that isotretinoin selectively affects neural crest cells by decreasing their cell-substratum adhesion.