A toxicologic and dermatologic review of 1-(2,4,4,5,5-pentamethyl-1-cyclopenten-1-yl)ethan-1-one when used as a fragrance ingredient is presented. 1-(2,4,4,5,5-Pentamethyl-1-cyclopenten-1-yl)ethan-1-one is a member of the fragrance structural group Alkyl Cyclic Ketones. These fragrances can be described as being composed of an alkyl, R1, and various substituted and bicyclic saturated or unsaturated cyclic hydrocarbons, R2, in which one of the rings may include up to 12 carbons. Alternatively, R2 may be a carbon bridge of C2-C4 carbon chain length between the ketone and cyclic hydrocarbon. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for 1-(2,4,4,5,5-pentamethyl-1-cyclopenten-1-yl)ethan-1-one were evaluated then summarized and includes physical properties, acute toxicity, skin irritation, mucous membrane (eye) irritation, skin sensitization, phototoxicity, and photoallergy data. A safety assessment of the entire Alkyl Cyclic Ketones will be published simultaneously with this document; please refer to Belsito et al. (Belsito, D., Bickers, D., Bruze, M., Calow, P., Dagli, M., Fryer, A.D., Greim, H., Miyachi, Y., Saurat, J.H., Sipes, I.G., 2013. A Toxicologic and Dermatologic Assessment of Alkyl Cyclic Ketones When Used as Fragrance Ingredients (submitted for publication)) for an overall assessment of the safe use of this material and all Alkyl Cyclic Ketones in fragrances.