We examined the relationship between pain and cognitive activity during the latent (≤ 3 cm), mid-active (5-7 cm), and transition (≥ 8 cm) phases of labor and the concomitant efficiency of the latent, active, and descent phases in 115 nulliparous women. Patients provided subjective pain ratings and described their thoughts during each of the three phases. Higher levels of pain during the latent phase of labor were predictive of longer latent (r=0.58) and active (r=0.50) phases of labor. Distress-related thoughts during latent labor were predictive of longer latent (r=0.31, P<.01), active (r=0.67), and second-stage (r=0.61) labor. We found no relationships between pain and cognitive activity measured during active labor and efficiency of active labor or second stage of labor. Pain and cognitive activity assessed during the latent phase were also prognostic of obstetric outcome. Thirteen of 19 women (68.4%) who reported “horrible” or “excruciating” pain required instrumental delivery, compared with eight of 27 women (29.6%) in the “discomforting” pain group. Subjects in the “distressrelated” cognitive group had 2.6 times the incidence of instrumental delivery, five times the incidence of abnormal fetal heart rate patterns, and four times the requirement for pediatric assistance for the neonate than subjects in the “coping” group. We conclude that latent labor is a critical phase in the psychobiology of labor and that pain and cognitive activity during this phase are important contributors to labor efficiency and obstetric outcome