The growth and the reproductive cycle of Littorina littorea were investigated in the Ria de Aveiro, Portugal, a country cited as the southern limit of the species distribution in Europe. Littorina littorea growth is well represented by the von Bertalanffy equation SH=24.6[1-e-0.69(t-0.70)] where SH is the shell height (distance from shell apex to the basis of the aperture measured in mm) and t is the number of winters: after periwinkles have reached a mean SH of 4.6 mm in their first winter they grow progressively to about 14.6 mm, 19.6 mm, 22.1 mm and 23.4 mm in the following four years and they attain the asymptotic mean maximum SH of 24.6 mm at the tenth year if they survive. Ripening of the gonads occurred from October to May but was more intense from December to February, whereas spawning extended from January to May in females and November to May in males. There was a seasonal shedding of the male penis at the end of the breeding season (summer) accompanying regression of the testis.