Objective To study the associations of patterns and duration of breastfeeding with the persistence of pelvic girdle pain 18 months after delivery.Design Longitudinal population study.Setting Norway, for the period 1999-2011.Population A follow-up of 10 603 women with singleton deliveries in the Norwegian Mother and Child Cohort Study who reported pelvic girdle pain at 0-3 months postpartum.Methods Data were obtained by four self-administered questionnaires and linked to the Medical Birth Registry of Norway.Main outcome measure Pelvic girdle pain, defined as combined anterior and bilateral posterior pelvic pain, 18 months after delivery.Results Eighteen months after delivery, 7.8% of respondents (829/10 603) reported pelvic girdle pain. Breastfeeding patterns at 5 months after delivery were not associated with persistence of pelvic girdle pain. The proportion of women with pelvic girdle pain 18 months after delivery increased as the duration of breastfeeding decreased (test for trend, P < 0.001). The estimated associations attenuated after adjustment for educational level, smoking status, and body mass index, but remained statistically significant for the association between 0 and 2 months of breastfeeding and persistent pelvic girdle pain (adjusted odds ratio 1.34; 95% confidence interval 1.03-1.75). The association of short breastfeeding duration with persistent pelvic girdle pain was only present in women with body mass index ≥25 kg/m 2 .Conclusions Breastfeeding was associated with a small beneficial effect on the recovery process of pelvic girdle pain in women with a body mass index ≥25 kg/m 2 . Among women with pelvic girdle pain, breastfeeding should be encouraged in accordance with the existing child-feeding recommendations.