- Objective To evaluate the relationship between duration of sexual abstinence and various characteristics of normal and subnormal semen. Design A retrospective study based on computerized data. Setting Fertility and IVF unit at a university medical center. Patient(s) Nine thousand, four hundred eighty-nine semen samples from 6,008 patients were analyzed according to the World Health Organization (WHO) manual and grouped according to sperm concentration (10 6 /mL) into severe (0.2–4 × 10 6 ), moderate (>4–10 × 10 6 ), and mild (>10–19.99 × 10 6 ) oligozoospermia, and normozoospermia (≥20–250 × 10 6 ) groups. Main Outcome Measure(s) In each group mean values of semen volume, sperm concentration, percentage of motile sperm and of normal morphology (according to WHO or Kruger criteria), total sperm count, and total motile sperm count per ejaculate were related to duration of abstinence. Result(s) Among the 3,506 oligozoospermic samples, the peak mean sperm motility of 30.3% was observed after 1 day of abstinence. Similarly, the mean percentage of normal morphology among mild-moderate oligozoospermic samples (n = 2,260) reached peak values of 7.4%–8.6% between 0–2 days of abstinence. The 5,983 normozoospermic samples showed a significant decrease in the percentage of sperm motility and normal morphology to mean values of 33.1% and 7.0%, respectively, on days 11–14 of sexual abstinence. Conclusion(s) Our data challenge the role of abstinence in male infertility treatments and suggest that to present the best possible semen samples, patients with male factor infertility should collect the semen after just 1 day of sexual abstinence. Patients presenting normal sperm analysis or sperm donors for cryopreservation purposes should be advised not to exceed 10 days of sexual abstinence.