Chalcides viridanus is a small skink endemic to Tenerife, the Canary Islands. This paper describes its annual reproductive cycle and sexual dimorphism by use of data from external measurements, dissection, and histological observation of gonads from monthly samples. Males were significantly larger than females in head-forelimb length, distance between forelimbs and hind limbs, tail width, and body mass. Male testes were largest in March, when most individuals showed active spermiogenesis, although no spermiation was observed. In April, the testes were somewhat smaller but showed seminiferous tubules and epididymis ducts with abundant sperm. In this month, female gonads and ovarian follicles were significantly enlarged, and vitellogenesis was evident. Oviductal embryos were found in May and June, and parturition took place at the beginning of August. Both testis mass in males and diameter of the largest oocyte in females were significantly correlated to abdominal fat body mass. We conclude that in C. viridanus both sexes exhibit seasonal changes in gonadal activity with synchronous development of both male and female gonads in the spring months.