Background. Although the incidence of pregnancy-associated pyogenic sacroiliitis is low, it is associated with significant morbidity and mortality. Timely diagnosis of the condition is challenging due to its nonspecific clinical features. Case. A 31-year-old primigravida had an uncomplicated pregnancy and labour. Postpartum, she developed persistent fever and debilitating hip pain on ambulation. White cell count was normal (7.3 × 10(9)/L) and C-reactive protein was elevated (468.4 mg/L). Streptococcus pyogenes was identified on vaginal swabs and blood cultures, and a pelvic magnetic resonance imaging scan revealed bilateral sacroiliitis. Conclusion. Pyogenic sacroiliitis is a potentially lethal cause of postpartum pain. It should be considered as a differential diagnosis even in low-risk women who present with debilitating pelvic pain in or around pregnancy, particularly when initial therapy appears unsuccessful.