Background: polycystic ovarian syndrome (PCOS) is a common cause of chronic anovulation; insulin resistance is considered an accepted mechanism for anovulation in PCOS especially in obese patients. Excess adrenal androgens are observed in patients with PCOS. An inverse relationship exists betweenDehydroepiandroste- rone sulfate (DHEAS) the body mass index (BMI). The use of cor- ticosteroids could improve ovulation in PCOS by decreasing serum androgen level. Objective: Evaluation of the efficacy of concomitant administra- tionof prednisolone and clomiphene citrate (CC) for the ovulation inductionin infertile lean women having CC-resistant polycystic ovarian syndrome(PCOS). Methods: Three hundred infertile lean women with clomiphene ci- trate (CC) resistant PCOS were randomly divided into two groups. Group 1:150 patient received clomiphene citrate (5 consecutive days of 150mg daily starting from the second day of the cycle) and pred- nisolone tablet (10 consecutive days of 10mg daily starting from the second day of the cycle). Group 2:150 patientreceived the same pro- tocol of CC plus placebo (10 consecutive days of 0.5mg folic acid daily starting from the second day of the cycle). All patientsshowed clinical manifestations of Hyperandrogenism (variable degree of hir- sutism and/or acne) where 18 patients were dropped out, and data on all relevant outcomes were available for 282 women and data were analyzed from 143 women in the CC-Prednisolone group and 139 in the CC-placebo group. The main outcome was the ovulation rate. Secondary measures included a number of follicles 18 mm or more, endometrial thickness on day of HCG administration and clinical pregnancy rate. Ovarian follicular response was monitored by trans- vaginal ultrasound and mid-luteal phase serum progesterone. HCG 10000 IU was given when at least one follicle measured 18 mm, and timed intercoursewas advised. Results: There were no statistically significant differences between groups as regards age, duration of infertility, BMI,the serum level of FSH, LH, TSH,and prolactin. The mediannumber offollicles ≥18 mm) at the time of HCG administration and the mean endometri-   al thickness wassignificantly higher in the prednisolone group than in the placebo group (P < 0.001).Similarly, there were significantly higher rates of ovulation (58.7% versus 23%) (P < 0.001) in the pred- nisolone group. The clinical pregnancy rate was significantly higher in the prednisolone group (p =0.006). Conclusion: The addition of prednisolone to CC in CC-resistant PCOS infertilelean patients was significantlyassociated with a higher ovulation rate, number of ovarian follicles ≥18 mm and en- dometrial thicknesson day of HCG administration, and number of patients becameclinical pregnant