Determining the age of individual wild canids that are older than one year is challenging. Cementum annuli analysis is con- sidered the most accurate technique for determining age in mammals. We compared age estimated by cementum annuli analysis to actual age for 62 kit foxes (Vulpes macrotis) of known age collected at the Naval Petroleum Reserves in California. The cementum annuli analysis was conducted by Matson’s Laboratory. The estimated age matched the actual age for 82.3% of the samples. No estimate deviated from the actual age by more than one year. The proportion of foxes aged correctly was significantly higher for foxes ≤ 1 year old (89.4%) compared to foxes ≥ 2 years old (53.8%). A higher proportion of foxes aged incorrectly died within 0.1 year of their birth date (63.6%) compared to foxes dying > 0.1 year of their birth date (3.4%). Nine of 11 foxes aged incorrectly were females indicating a potential sex bias in aging accuracy. Cementum annuli analysis provided reasonably accurate estimates of age (in years) for kit foxes. Errors did occur and were most common among foxes ≥ 2 years old, foxes dying around the time of their birth date, and possibly females. Researchers should be cognisant of and account for these potential sources of error when interpreting results of cementum annuli analysis for kit foxes and possibly other fox species as well.