The age, growth and reproduction ofChondrostoma polylepis willkommi, an endemic cyprinid from the Iberian Peninsula, was studied for 2 years in a seasonal stream in the Guadalquivir River basin. Annual growth was low. Maximum ages observed were 5+ in males and 7+ in females. There was no significant difference in growth between sexes. Seasonal growth period started in May and continued for 2 to 6 months depending on age. The mean lengths of 1 + and 2+ age‐groups decreased once the growth period had finished, probably related to reproductive stress and adverse ecological conditions, and this could explain the occurrence of Rosa Lee's phenomenon. Both sexes matured at the end of their second year of life (1+). There was a significant difference from 1: 1 in the overall sex ratio of 334 males to 464 females. Reproductive period started in March and lasted until May.Ch. p. willkommiwas a multiple spawner that released two batches of eggs per female each year. The regression between fecundity (F) and fork length (l., mm) was:F=6.20 103L.2.78. In females from age 2 + onwards, relative annual investment in somatic growth and reproduction was equivalent, implying that the same energy was allocated to reproduction as to maintenance/growth. Compared with otherCh. polylepispopulations, the life‐history patterns of this population, located in a small and seasonal stream in a southern latitude, were characterized by a low annual growth, a trade‐off between reproduction and growth/maintenance, early maturity, low number of age‐groups and high fecundity from multiple sp