We aimed to ascertain the chronologic age at which these sonographic measurements begin to show a significant difference. The study included 100 women (78, aged 19-44 and 22, aged 45-50) menstruated spontaneously and without thyroid disease, diabetes mellitus, hyperprolactinaemia, hypogonadotropic hypogonadism or polycystic ovary syndrome and any gynaecologic surgery. They all underwent sonographic measurement of total antral follicle (TAF) count and mean ovarian volume (MOV) on the second or third days of menstrual cycle. Then, the women were assigned to 5 groups: group 1, 19–24 years; group 2, 25–29 years; group 3, 30–37 years; group 4, 38-44 years; and group 5, 45-50 years. There was a significant association between chronological age and TAF number (r2 = 0.328, p < 0.001). No significant difference was noted in TAF number among the first three groups (r2 = 0.58, p > 0.05). TAF number was significantly different between groups 3 and 4 (Z: -3.463, p < 0.001), but not between groups 4 and 5 (Z: -1.698, p > 0.05). There was a significant relationship between chronological age and MOV (r2 = 0.149, p < 0.001). MOV values did not show a significant difference among the first 4 groups (r2 = 0.58, p> 0.05; r2 = 7.87, p > 0.05 respectively). The MOV of group 5 was significantly different from those of groups 1, 2, 3, and 4 (Z: -2.75, p < 0.01; Z: -4.351, p < 0.01; Z: -2.722, p < 0.01; and Z: -2.829, p < 0.01 respectively). In conclusion, the TAF count decreases significantly beginning at 38 years of age, while MOV decreases significantly beginning at 45 years of age. Thus, there is no significant decrease in the ovarian follicular reserve until the age of 38 years, or in the ovarian volume until the age of 45 years.