Although fibroids constitute the most common tumour in women of reproductive age, it is remarkable how very rarely they cause acute complications. However, when they do occur, the acute complications can cause significant morbidity (very occasionally, mortality), profoundly affecting a woman's quality of life. The complications include thrombo-embolism, acute torsion of subserosal pedunculated leiomyomata, acute urinary retention and renal failure, acute pain caused by red degeneration during pregnancy, acute vaginal or intra-peritoneal haemorrhage, mesenteric vein thrombosis and intestinal gangrene. The obstetrician will be most familiar with red degeneration and acute urinary retention, both of which tend to occur in association with pregnancy. It is difficult to quote an incidence rate for these acute complications as they are rare, and most are reported as cases or case series in the literature. The majority (except red degeneration, acute urinary retention and thrombo-embolism) presents as an acute abdomen and requires urgent exploratory surgery. The differential diagnosis would include twisted adnexa, ruptured ectopic pregnancy, haemorrhagic corpus luteum or follicular cyst, whilst that of the pelvic mass would be ovarian or endometrial carcinoma, uterine sarcoma or leiomyoma and, rarely, ovarian fibroma. Deep vein thrombosis is usually due to pelvic venous compression, and while some have advocated that its occurrence in association with a fibroid mass should be an absolute indication for hysterectomy, sophisticated use of radiological adjuncts at surgery, such as 'umbrellas' and haematological support with appropriate anticoagulation, could enable uterine-preserving surgery. The diagnosis of fibroids as a cause of acute urinary retention should be one of exclusion. The treatment of the acute fibroid in pregnancy is of course conservative, definitive treatment being postponed until postpartum.