Background: Although topically applied all-trans-retinoic acid (tretinoin) undergoes minimal absorption and adds negligibly to normal endogenous levels, its safety in humans is occasionally questioned because oral ingestion of retinoids at therapeutic levels is known to entail teratogenic risks. Objective: To assess the actual potential for developmental toxicity from treatment with topical tretinoin. Methods: Risk assessments were conducted on four known human developmental toxicants (valproic acid, methotrexate, thalidomide, and isotretinoin) and a potential developmental toxicant (acetylsalicylic acid). The margin of safety for each chemical was calculated from the ratio of animal no-observed adverse effect levels to human lowest-observed adverse effect levels or estimated exposure doses. Results: The derived safety margin of more than 100 for topical tretinoin (with 2% absorption) contrasted sharply with the near unity values for valproic acid, methotrexate, thalidomide, and isotretinoin and was longer than that for acetylsalicylic acid. Conclusion: These data support other epidemiologic and animal data that topical tretinoin is not a potential human developmental toxicant. (J Am Acad Dermatol 1997;36:S86-S90.)