We conducted a prospective study of conservative treatment in 21 young nulliparous women with grade (G)1 endometrial cancer stage IA (11) or atypical complex hyperplasia (10). All were treated with a low-dose cyclic natural progestin therapy (200 mg/day from day 14-25) and encouraged to attempt pregnancy immediately. No adverse therapy-related effects were recorded. Overall response rate to progestin therapy was 57%. Nine women conceived (43%). There were 13 pregnancies, of which 13 were spontaneous and 8 were in women with persistent disease or partial response to hormonal treatment. Three additional complete responses were observed after delivery. Only women with known primary infertility or severe polycystic ovary syndrome showed inadequate pregnancy rate. Fifteen women underwent definitive surgery after enrolment (median 27 months, range 3-56 months). All 21 women are alive and disease free after a median follow up of 98 months.