A toxicologic and dermatologic review of 3-methyl-1-cyclopentadecanone when used as a fragrance ingredient is presented. 3-Methyl-1-cyclopentadecanone is a member of the fragrance structural group macrocyclic ketones and derivatives. The fragrance ingredient described herein is one of 11 structurally diverse C15, C16 and C17 compounds that include three saturated and eight unsaturated ketones. For the latter, the double bond is not adjacent (in conjugation with) to the ketone group. This review contains a detailed summary of all available toxicology and dermatology papers that are related to 3-methyl-1-cyclopentadecanone and is not intended as a stand-alone document. Available data were evaluated, then summarized, and includes: physical properties, acute toxicity, skin irritation, skin sensitization, phototoxicity, toxicokinetics, repeated dose, and genotoxicity data. A safety assessment of the entire macrocyclic ketones and derivatives will be published simultaneously with this document. Please refer to Belsito et al. (2011) for an overall assessment of the safe use of this material and all macrocyclic ketones and derivatives in fragrances. Belsito, D., Bickers, D., Bruze, M., Calow, P., Dagli, M., Fryer, A.D., Greim, H., Hanifin, J.H., Miyachi, Y., Saurat, J.H., Sipes, I.G., 2011. A Toxicologic and Dermatologic Assessment of Macrocylic Ketones and Derivatives When Used as Fragrance Ingredients.