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.