Objectives: study the effect of simple trans-vaginal aspiration of chocolate cyst on pregnancy rate among the infertile patients diagnosed with ovarian endometrioma less than 6 cm. Study design: controlled clinical trial. Subjects and methods: 100 cases recruited for the trial and divided into two groups Group one: the intervention group 50 cases diagnosed with ovarian endometrioma undergone chocolate cyst aspiration in zinat alhayat hospital after consultation and written consent. Group two: 50 controls comprises the nonintervention group and cyst left without aspiration. All cases and controls done AMH, antral follicle count, stromal flow resistive index and CA 125 at the first month, Cases and controls followed in a period of 3 month the first month passed without induction. Second and third months ovulation was induced in both groups with HMG meriofert 75 unit at day 3,5and 7 then follicular growth monitored and ovulation triggered by HCG, pregnancy diagnosed with quantitative HCG and followed to the clinical pregnancy rate with viable fetal pulsations at 6 weeks. Outcome measures: CA 125 antral follicle count stromal flow resistive index, deep dyspareunia and clinical pregnancy rate. Results: regarding antral follicle count a good count of 12 found in the intervention group in 35 out of 50 compared to 20 out of 50 in the control group with p value 0.002, regarding significant stromal flow resistive index of 0.5 there were 40 out of 50 in cases and 25 out of 50 in controls with p value of 0.001,a statically significant difference with p value of 0.001 was found retrograding deep dyspareunia ,and clinical pregnancy observed in 30 cases out of 50 compared to 15 out of 50 in controls with p value of 0.002. Conclusion: simple trans-vaginal aspiration of ovarian chocolate cyst can improve ovarian response and increase clinical pregnancy rate better than conservative management.