Objective: To study the associations between parental subfecundity, assessed by time to pregnancy and use of medically-assisted reproduction, and reproductive health of young men.Design: Cohort study.Setting: Denmark.Patient(s): A total of 1,058 men in the Fetal Programming of Semen quality cohort, a subcohort of the Danish National Birth Cohort. Intervention(s): From 2017-2019, men were recruited and provided semen and blood samples. Information on parental time to pregnancy and use of medically-assisted reproduction (including type of treatment) as well as demographic, health, and lifestyle factors were available. We estimated the crude and adjusted relative percentage differences with 95% confidence intervals (CIs) in the outcomes according to time to pregnancy and use of medically-assisted reproduction, using multiple adjusted negative binomial regression analysis.Main Outcome Measure(s): Semen characteristics (semen volume, sperm concentration, total sperm count, sperm motility, and morphology), testicular volume, and reproductive hormone levels (follicle stimulating hormone, luteinizing hormone, testosterone, estradiol, sex hormone-binding globulin, and free androgen index). Result(s): Overall, semen quality and levels of reproductive hormones were not lower among sons of subfecund parents reporting a time to pregnancy >6 months or use of intrauterine insemination. Sons conceived after in vitro fertilization or intracytoplasmic sperm injection, had a higher semen concentration (29%; 95% CI, -7%-79%) and a higher percentage of sperm with normal morphology (20%; 95% CI, -8%-56%), but with 95% CI overlapping the null. Moreover, these sons had slightly higher estradiol levels (30%; 95% CI, 7%-57%). The absolute differences seen were small, and the clinical significance of these differences are unknown.Conclusion(s): We found no major difference in semen quality or reproductive hormones in sons conceived by subfertile couples or with the use of medically-assisted reproduction. (Fertil Sterile 2022;118:671-78. (c) 2022 by American Society for Reproductive Medicine.) El resumen esta disponible en Espanol al final del articulo.