OBJECTIVES: To characterise and document the progression of idiopathic renal haematuria in a large cohort of medically managed UK dogs. MATERIALS AND METHODS: Retrospective study of 41 client-owned dogs with confirmed (n=14), or suspected (n=27) idiopathic renal haematuria from 4 UK-based referral centres. Clinical findings and outcomes of dogs (2001 to 2018) were determined from the review of medical records and telephone follow-up. RESULTS: Median survival time from diagnosis was long [1482 (152 to 1825) days] irrespective of treatment and clinical response. Only 1 case was euthanased due to idiopathic renal haematuria, and anaemia or azotaemia occurred infrequently. In total, 25 dogs received angiotensin-converting enzyme-inhibitor or angiotensin receptor blocker therapy, of which 23 received benazepril [0.44 (0.19 to 0.82) mg/kg/24 hours], two received enalapril (0.40 and 0.78 mg/kg/24 hours) and one received telmisartan (1 mg/kg/24 hours). In cases with follow-up urinalyses, complete resolution of haematuria was documented in eight of 19 (42%) dogs following angiotensin-converting enzyme-inhibitor/angiotensin receptor blocker treatment, with partial improvement in five of 19 (26%) and no improvement in six of 19 (31%). Conversely, of the two untreated dogs where outcome was available, one had partial improvement and the other had no improvement. CLINICAL SIGNIFICANCE: In this study, idiopathic renal haematuria was associated with a good prognosis and low complication rate. Resolution or improvement in haematuria occurred in both angiotensin-converting enzyme-inhibitor/angiotensin receptor blocker-treated and untreated dogs, indicating that further studies are required to evaluate the effectiveness and safety of these interventions.