Demographic data are sparse for Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri; YCT). Data for YCT in the spawning run (spring; 29 years) of a Yellowstone Lake tributary or caught in gill nets set (fall; 30 years) at established lake locations between 1977 and 2007 were examined. Female proportion in runs averaged 0.61 but was 0.48 among gillnetted “prespawner” YCT (i.e., mature fish whose excised gonads indicated the fish would have spawned the next year). Maturity proportion-total length (TL) relationships for gillnetted female and male YCT were logistic-shaped and similar in their inflection points; maturity onset occurred at 200–250 mm TL; ∼95% of YCT ≥ 400 mm TL were mature and ∼70% were prespawners. Fecundity was positively associated with YCT TL. Accuracy of scale-based YCT ages was affected by a frequently overlooked scale annulus and an inability to unequivocally identify fish of a single cohort on the basis of scale characteristics using associated, recognized ageing criteria for this population. Temporal differences in fits of a modified von Bertalanffy growth model to YCT TL at capture and scale-based age probably resulted from ageing errors evident among successive, annual scale analysts rather than differences in YCT growth. Nevertheless, when the age estimates of one, long-term analyst were used in analyses, the estimated growth parameters L_∞ and ω; were concordant with empirical observations of the maximum TL of YCT and TL of age-1 YCT in Yellowstone Lake, respectively. The demographic relationships and linking, parameterized growth model provide a useful foundation for age-structured population modeling.