Ovarian follicular development and ovulation were studied by ultrasound scanning in the Mexican viviparous lizard Barisia imbricata. A linear ultrasound unit with variable capacity from 5 to 10 MHz was used. Vitellogenic follicle diameters ranged from 3.3 to 9.8 mm and were present in the lizards between September and December. Also, corpora lutea and uterine eggs were identified. The ultrasound is an excellent non-invasive technique to determine seasonal reproductive changes and can be combined with other techniques to monitor the reproductive process.