We aimed to describe clinical course of myelolipoma and to identify predictors of tumour growth and need for surgery. A retrospective study. Consecutive patients with myelolipoma. A total of 321 myelolipomas (median size, 2.3 cm) were diagnosed in 305 patients at median age of 63 years (range, 25-87). Median follow-up was 54 months. Most myelolipomas were incidentally detected (86%), whereas 9% were discovered during cancer staging and 5% during workup of mass effect symptoms. Thirty-seven (12%) patients underwent adrenalectomy. Compared to myelolipomas <6 cm, tumours ≥6 cm were more likely to be bilateral (21% vs 3%, P < .0001), cause mass effect symptoms (32% vs 0%, P < .0001), have haemorrhagic changes (14% vs 1%, P < .0001) and undergo adrenalectomy (52% vs 5%, P < .0001). Among patients with ≥6 months of imaging follow-up, median size change was 0 mm (-10, 115) and median growth rate was 0 mm/y (-6, 14). Compared to <1 cm growth, ≥1 cm growth correlated with larger initial size (3.6 vs 2.3 cm, P = .02), haemorrhagic changes (12% vs 2%, P = .007) and adrenalectomy (35% vs 8%, P < .0001). Most myelolipomas are incidentally discovered on cross-sectional imaging. Myelolipomas ≥6 are more likely to cause mass effect symptoms, have haemorrhagic changes and undergo resection. Tumour growth ≥1 cm is associated with larger myelolipoma and haemorrhagic changes. Adrenalectomy should be considered in symptomatic patients with large tumours and when there is evidence of haemorrhage or tumour growth.