Personality may influence sleep in perinatal women. A follow-up study was conducted among 3,752 pregnant, then postpartum women at Akershus University Hospital, Norway. The Big Five personality dimensions were measured by the Mini-International Personality Item Pool in week 17 of pregnancy. Insomnia was measured by the Bergen Insomnia Scale in pregnancy week 32 and 8 weeks postpartum, along with self-reported sleep times. The Edinburgh Postnatal Depression Scale measured depression, and the Hopkins Symptom Checklist measured anxiety. Adjusted for current anxiety, depression, and demographic variables, the personality traits Neuroticism and Agreeableness were associated with insomnia in pregnancy. No personality traits were associated with postpartum insomnia. Extraversion was associated with longer postpartum sleep duration and better sleep efficiency, and Agreeableness with shorter sleep duration.