A published range of reactions to the tuberculin skin test (TST) using mammalian (human) old tuberculin (MOT) in a population of Mauritius origin Macaca fascicularis in US laboratory animal medicine does not exist. The objectives of this report are to quantify the reactions among juvenile, adolescent, and male adult cynomolgus macaques and to provide the laboratory animal medicine practitioner with a reference range of reactions to MOT in Mauritian juvenile macaques. Monkeys in a US foreign animal quarantine must be tested negative for mycobacterial infection including Mycobacterium tuberculosis (Mtb) using MOT as required by the CDC Division of Global Migration and Quarantine. The TST relies on visual observation post injection of an individual animal’s reaction or nonreaction. During 2017, 933 Mauritius origin macaques from one supplier were quarantined in nine separate cohorts in our facility. 848 or > 90% of the animals were juveniles between 1.5 to 3 years of age, comprised of 425 males and 423 females. The population also included 46 adolescents (21 males, 25 females) and 39 adult males. A total of 33 TST sets were performed on the nine cohorts, resulting in 3418 individual TSTs being administered. 1595 (46.6%) injections were made in juvenile males and 1529 (44.7%) in juvenile females. A total of 172 reactions to the TST were recorded at the final assessment completed at the 72-hour post injection time point from all animal ages and sexes. 162 reactions (94.2% of all reactions) occurred in juvenile animals, consisting of 96 bruises (59.3% of all juvenile reactions) in males and 58 bruises (35.8% of all juvenile reactions) in females. Bruising was the most common reaction in juvenile animals and in all animals regardless of age or sex. Bruising occurred within all 33 TST sets ranging from a low of 0% to a high of 30% in male juveniles and a low of 0% to a high of 17% in female juveniles. Bruising was the only finding in the adolescents and adult males. Erythema was observed only in juvenile animals, two males and three females. Generalized eyelid edema was observed only in juvenile animals, one male and one female. These animals had concurrent erythema in the affected eyelid. Animals with generalized eyelid edema and erythema are considered suspect for active tuberculosis and warrant further diagnostics. In this report, the most observed reaction among all age groups and sexes was bruising. Erythema and edema were rarely observed. Only juvenile animals were observed with either erythema, edema or both.