We report 2 cases of squamous dysplasia associated with long-term hydroxyurea therapy. The association between hydroxyurea and multiple aggressive squamous cell carcinomas, Bowen's disease, and multiple actinic keratoses in sun-exposed areas after a variable latency period has been increasingly reported. On reviewing the literature, 17 cases were identified and are reviewed, with emphasis on possible pathogenetic mechanisms of carcinogenicity. Squamous dysplasia, a precursor state to a more aggressive condition of multiple squamous cell carcinomas in photoexposed areas, should be added to the well-known cutaneous toxicities of hydroxyurea therapy.