Repeat breeding in dairy cows results in large economic loss; however, the etiology of this phenomenon remains elusive. The objectives were to examine the behavioral and endocrine patterns around estrus, and the characteristics of preovulatory follicles in repeat breeder (RB) vs. normal (CTL) cows. The CTL cows were >60 d in lactation, cycling and not inseminated, and a cow was considered as RB if it did not become pregnant after at least 4 successive inseminations (average 7.0 ± 2.0), with normal intervals. A total of 27 and 31 cycles in 12 RB and 18 CTL cows, respectively, were synchronized. Data were analyzed as repeated measurements by the MIXED procedure of SAS, and the model included the effects of treatment, cow and cluster. Behavioral estrus and ovulation were observed in 81.5 and 83.8% of the synchronized cycles in the RB and CTL cows, respectively. The RB and CTL cows had similar estrus durations of 21.4 and 19.6 h, respectively, but estrus was more intense in the RB, as indicated by numerically higher overall activity indexes and higher peak neck activity. The interval from PG injection to estrus onset (i.e., proestrus) was 8.2 h shorter in RB than in CTL cows (47.9 and 56.1 h, respectively; P < 0.007), but the average preovulatory follicle size was similar. Plasma estradiol (E₂) concentration at peak was numerically higher (21%) and the AUC tended to be higher in the RB than in the CTL cows. Also, LH secretion during the period from 18 to 3 h before the LH peak was lower in RB than in CTL: 2.5 and 4.6 ng/mL, respectively (P < 0.01). In another study, 16 preovulatory follicles (8 CTL and 8 RB) were aspirated 48 h after PG injection. No differences were observed in androstenedione and progesterone (P₄) in follicular fluid, but concentrations were 1.7 fold higher (P < 0.005) and E₂/P₄ ratio tended to be higher (P < 0.07) in RB than in CTL cows. In conclusion, better estrus expression, similar follicular diameter and higher E₂ in RB indicate that the etiology of repeat breeding lies beyond these parameters. However, short proestrus and subdued LH concentrations before the LH peak, which could impair oocyte competence and development, are first reported in RB cows.