Age and growth of southern blue whiting Micromesistius australis are studied. Sagitta otoliths from 3650 specimens were used for age determination. These were taken during research surveys and commercial catches in the South West Atlantic during 1994 and 1995. The size of fishes ranged from 17 to 60 cm total length, corresponding to ages 0 to 23 years. Females attained a greater asymptotic length (L_∞ 59.74 cm) than males (L_∞ 54.72 cm). Comparison of growth curves by the likelihood ratio showed that the differences among females and males were due to the asymptotic length, while the other parameters (K and t0) were not statistically different. The mean weight-at-age, mean length-at-age, and total mortality (Z) were estimated. Growth parameters estimated by sex in the period 1994-95, mean size per age group, and the number of individuals per age in the catches show differences with those calculated when the population was in the early stage of exploitation. A predominance of 2 to 9 year old individuals was observed in the total catches in 1994-1995, whereas in the beginning of the fisheries total catches were basically fish 15 to 19 years old.