Urinary tract infections investigated in hospital show a series of clinical and etiological features, especially concerning antibiotic sensitivity, determined by the recurrent pattern of these disease, which often determines severe urinary or general complications. We considered 36,136 urine samples belonging to patients admitted in hospital with history or symtomatology of urinary infection. We noted the following: Urine bacteriological investigation is one of the most asked for laboratory examinations in hospital, having a diagnostic significance (more than 10(5) cfu/ml) in only 15,45% of cases. The etiological patterns, though similar to those registered in ambulatory investigations, present a series of characteristics like: decreased percent of isolation of Enterobacteriaceae - 76.14%, compared to 98.90%, increased proportion of some groups of Gram-negative bacilli highly-resistant to antibiotics, such as Pseudomonas and Acinetobacter and of some groups of Gram-positive cocci--especially group D streptococcus. Accordingly, the sensitivity patterns denote the decrease of the proportion of strains that are sensitive to "regular" antibiotics, this phenomenon implying the use of recent antibiotics, more costly. Once again we point out to the necessity of conducting antibiotherapy by means of evaluating sensitivity during therapy.