Abstract: This study evaluated the phenotypic trends for wool and growth traits of the fine Merino genetic nucleus in Uruguay. Data were collected from one?year?old lambs over a twenty?year period(1999?2018). The overall aim of the selection flock was to reduce fiber diameter with concomitant increases in fleece and live weights. Traits analyzed included fiber diameter (FD), greasy fleeceweight (GFW), coefficient of variation of FD (CVfd), staple length (SL), scoured yield (SY), live weight post?shearing (LW), eye muscle area (EMA) and fat thickness (FAT). Data from approximately5300 one?year?old male and female lambs were analyzed. During the study period, FD decreased by approximately 3 ?m, whereas GFW and LW increased by at least 0.5 and 3.0 kg, respectively.There were interactions between the sex of the individual and the year for all wool traits. Except for FAT, all other traits were affected by the dam age. This study indicates that the selection program applied in the fine Merino genetic nucleus over a twenty?year period resulted in reductions in FD and increases in GFW and LW. Therefore, the results indicate it is possible to produce ultrafine wool in semi?extensive grazing systems without compromising other economically relevant traits in one?year?old lambs.