ABSTRACT. Laerum E, Larsen S (Institute of General Practice, University of Oslo, Oslo, and MEDSTAT, Center for Administration Design and Statistical Analysis in Medical Research, Strømmen, Norway). Is it possible to characterize recurrent urinary stone formers who benefit from thiazide prophylaxis? Application of discrimination analysis. Acta Med Scand 1987; 221: 103–8. Twenty‐three patients with recurrent urinary stones have been treated for 12–54 months with hydrochlorthiazide and 25 with placebo. Discrimination analysis was performed in order to distinguish patients with new stone formation (non‐responders) from those without stone recurrence (responders) during the treatment. The discriminant function classified 16 out of 18 responders as such and 5 non‐responders as such by using a combination of the three intital varibles urinary pH, 24‐h urine volume and serum phosphate. Eighteen other analysed variables and patient factors did not contribute to this discrimination. By using “leaving‐one‐out‐technique”, the probability for erroneously classifying a patient increased from 9 to 17%. Applying the discriminant function on the group receiving placebo, 92% of these patients were classified as responders to thiazide. It is concluded that discrimination analysis may give valuable information in charcterizing patients who will benefit from a special therapy.