Unplanned, urgent initiation of renal replacement therapy (RRT) is associated with poorer outcomes than planned initiation. However, in many services worldwide, substantial numbers of patients still do not begin treatment electively. The aim of this study was to identify numbers of and possible risk factors for, patients starting unplanned RRT despite being known to renal services for > or =4 months.A retrospective survey of electronic and medical records was conducted of patients starting RRT in a large regional UK renal network in 2003. Data extracted included information on demographic, biochemical and treatment factors. Patients were classified as known acute (starting dialysis urgently yet known to renal services > or =4 months) or elective (starting RRT in a planned manner with a fistula or peritoneal dialysis catheter). Urgent dialysis was defined as starting either with a haemodialysis catheter or as an inpatient. Logistic regression was used to identify factors predicting an urgent dialysis start.Data from 109 of the 126 eligible patients were included; 60 elective, 49 known acute. Reasons for presenting as known acute were illness (21), service (24) and patient related (17). More than one reason was identified for 11 patients. The known acute group had more severe anaemia and lower glomerular filtration rates. Fewer known acute patients had attended dedicated predialysis clinics (90% increased odds of known acute start for non-attendance, P = 0.001) and patient dialysis information sessions (P = 0.020). Dialysis counselling had begun sooner in elective patients (P = 0.003). Odds of an urgent dialysis start increased by 4% with each year of age (P = 0.024).Early dialysis education and predialysis clinic attendance were associated with greater likelihood of elective dialysis initiation. Further studies are required to determine the cost effectiveness of these interventions, but services that initiate RRT urgently in a high proportion of patients should consider improving predialysis clinic attendance and early dialysis education.