The aim of this study was to investigate if individuals born with sub-optimal birth characteristics have reduced probability of reproducing in adulthood. less thanbrgreater than less thanbrgreater thanUsing population-based registries, the authors included 522 216 males and 494 692 females born between 1973 and 1983 and examined their reproductive status as of 2006. Outcome measure was the hazard ratio (HR) of reproducing. Adjustments were made for socio-economic factors. less thanbrgreater than less thanbrgreater thanMales and females born very premature displayed a reduced probability of reproducing [HR 0.78, 95 confidence interval (CI): 0.700.86 for males; HR 0.81, CI: 0.750.88 for females]. Likewise for very low birthweight (HR 0.83, CI: 0.710.95 for males; HR 0.80, 95 CI: 0.720.89 for females). Individuals born large for gestational age (LGA) displayed no significant changes. Males born small for gestational age (SGA) had a 9 lower reproductive rate (CI: 0.890.94) and that reduction increased as the individuals aged. Women born SGA tended to start reproducing at an earlier age. less thanbrgreater than less thanbrgreater thanThe results suggest that being born with low birthweight, premature or SGA (for males) is associated with a reduced probability of reproducing as an adult. LGA shows no statistically significant relationship with future reproduction.