A prospective study to evaluate the microbiological efficacy of antimicrobial treatment for urinary tract infection (UTI) was performed in 64 catheter-free spinal cord injured (SCI) patients who were visited monthly by a public health nurse who collected urine for culture and urinalysis, Patients also mailed urine dip slides for weekly bacterial counts, UTI was defined as a culture yielding ³ 100,000 colonies/mL Treatment was given to asymptomatic patients only if pyuria (³ 10 urinary leukocytes/high powered microscopic field) was present, Initial treatment was for 7-14 days (group 1), When it became apparent during the study that eradication was difficult and relapse or reinfection frequently occurred within a short time after cessation of antibiotic, a second treatment course of ³ 28 days (group 2) was given, By the end of the study, in which all patients were followed for a minimum of 30 days post treatment, 39/42 (93%) cases in group 1 and 11/13 (85%) in group 2 who had initial eradication, had relapsed or become reinfected. The median number of days and standard error for group 1 to relapse or become reinfected was 16 ± 2.5, and for group 2 it was 27 ± 6. Development of drug resistance was documented when bacteria isolated prior to any treatment were compared with strains isolated after ³ 28 days of antibiotics. In this study, urine sterility was achieved in a minority of treated UTIs and was relatively short lived. Advisability of treating asymptomatic UTI following SCI is questionable from both a medical-economic and microbiologic standpoint, particularly in view of the likelihood of inducing multidrug resistance with prolonged antibiotic exposure. © 1993 International Society of Paraplegia.