Data from two experiments were used to study the relationship between weaning-to-estrus interval (WEI, varying from 3 to 6 d) and the duration of estrus, the interval from onset of estrus to ovulation and fertilization results at 120 h after ovulation, in 201 multiparous sows. An increase in WEI resulted in a decrease in the duration of estrus (Duration of estrus (h) = [81 (exp1) or 88 (exp2)]-.33 x WEI, R2 = .25, P < .001) and a decrease in the interval from onset of estrus to ovulation (onset estrus to ovulation (h) = [54 (exp1) or 59 (exp2)]-.20 x WEI, R2 = .23, P < .001). Sows that were inseminated between 0 and 24 h before ovulation showed consistent high fertilization results (91% normal embryos), irrespective of WEI. Sows that were inseminated outside this range showed an increased proportion of unfertilized eggs (P < .001). This increase occurred similarly in all weaning to estrus intervals. These results suggest that negative effects of a longer WEI on subsequent litter sizes and farrowing rates as described in literature might be a result of suboptimal timing of insemination relative to ovulation and not of poor fertility in these sows.