Pearl oysters (Pinctada mazatlanica) were collected by SCUBA and skin diving in a unexploited bed off Pájaros Island, Golfo de Nicoya, Costa Rica (n=229), from April to August 1993. Shell height was 21.4-147 mm. The relationships shell height: weight, and shell height: width were: A=0.1904 Pt+ 52.6354 and A=2.5734, respectively. The relationship between shell length and height was isometric, whereas the other relationships indicate allometric growth.