It is well known that uterine leiomyomas shrink after the menopause. Fibrosis is the most common type of myomatous degeneration, but its relationship to menopause has not been studied. We evaluated fibrosis in 237 small myomas (< 1 cm) in relation to menopause, tumor size, intrauterine location, and patient age. Substantial fibrosis was seen in 33 (21%) of 159 small premenopausal myomas versus 39 (50%) of 78 small postmenopausal myomas (P < 0.001). This relationship was even stronger for women between 40 and 60 years of age: 27 (21%) of 126 premenopausal women versus 12 (71%) of 17 postmenopausal women (P < 0.001). Only 23 (23%) of 101 2- to 4-mm myomas had substantial fibrosis versus 45 (40%) of 112 5- to 9-mm myomas (P < 0.01). Small postmenopausal myomas that were inframucosal had less frequent fibrosis (3 [27%] of 11) than their intramural and subserosal counterparts (36 [54%] of 67) (P = 0.05). There was a significant increase in seedling myomas (fully cellular myomas < 1 cm) from postmenopausal women aged 60 to 70 years (13 [35%] of 37) compared with younger postmenopausal women (1 [6%] of 17) (P < 0.01). We conclude that fibrosis is strongly associated with menopausal status in small uterine myomas, that size and location are also related to fibrosis in small myomas, and that seedling myomas may arise after the menopause. Our interpretation of these findings is that the most likely cause of fibrosis in small myomas is senescence and that there may be heterogeneity in the molecular basis of senescence.