Weight-length relations were estimated for Atlantic horse mackerel from the Portuguese coast, from 2000 to 2007. A total of 31240 individuals (16549 females and 14691 males) ranging from 11.7 to 43.6 cm total length were sampled and W-L relations were analysed by year, month, season, sex and fishing region. The estimates of the parameter b of the relation indicate an isometric growth for both sexes. Values of b varied along the year, with unexpected higher val- ues from November to March, which is, however, similar to the references of Lucio & Martin (1989). The values of allometric parameter b obtained in this study are similar to the ones reported in the NE Atlantic and Mediterranean Sea and to the ones available for the Portuguese coast.