Microscopic haematuria is a common finding in young men. Controversy exists as to its significance and how it is best investigated. A prospective study of 100 young men under the age of 40 with microscopic haematuria has been performed. A positive diagnosis was made in 32 patients. Cystourethroscopy was of diagnostic value in only 3 patients and of therapeutic value in a further 3. It was concluded that cystourethroscopy is of minimal diagnostic value in young men with microscopic haematuria. Its routine use is unnecessary and should be reserved for those patients in whom investigation suggests that a treatable cause may be found in the lower urinary tract.