The age and growth of sand smelt, Atherina boyeri (Risso 1810), in the Mar Menor (SE Iberian Peninsula) were studied in samples taken from catches of local fishermen obtained between November 1997 and September 1998. The maximum lengths were 94 mm (FL, fork length) in females and 87 mm (FL) in males. Age determination based on scale readings and validated by length frequency analysis shows that the population has a 3-year life cycle. Females were significantly longer than males in each of the age classes. Both sexes of the sand smelt grow allometrically (b = 3.113 males; b = 3.043 females) and attain approximately 56.2% of their maximum fork length in their immature first year, after which the annual growth rate drops quickly. The highest growth rate was observed from winter to spring (G (L) = 16.01 males 1+; G (L) = 11.25 males 2+; G (L) = 17.18 females 1+; G (L) = 9.62 females 2+). The condition cycles were similar for both sexes, with a minimum in June-July and two maximums in April and November.