To estimate the weight-length relationship, determine age, and describe growth of the finescale triggerfish, Balistes polylepis Steindachner, 1876, 552 specimens were measured and weighed, and 318 first dorsal spines were collected from the artisanal catch in Mazatlán, Sinaloa, Mexico, between October 2000 and October 2001. Fish ranged between 16 and 53 cm in total length (TL), and distribution was biased toward small sizes. Age was assigned according to the number of opaquehyaline bands in spines, identifying seven age groups (1–7), with age groups 2, 3, and 4 jointly representing over 80% of the collection. The von Bertalanffy model was adequately fitted to the age-TL data and accounted for 91% of the variation in TL. Parameters were estimated as TL_∞ = 55:8 cm; K = 0.17 yr⁻¹, and t₀ = −1:7 yr. The total weight (TW ) of the finescale triggerfish ranged between 75 and 2,200 g, and the TW-TL relationship showed a negative allometric growth (b = 2:7). These results are the first reported for age and growth of this species.