The purpose of this study was to describe resistance patterns of infecting organisms and determine risk factors for multidrug resistance in patients with urinary tract infections. Retrospective case series of 435 patients age > or =16 with urinary tract infection. Multidrug resistance was defined as resistance to > or = two classes of antibiotics. Demographic, historical, and microbiological data were collected. Univariate analysis and multivariate logistic regression were used to determine risk factors for multidrug resistance. Multidrug resistance was seen in 37% of isolates. Univariate analysis revealed numerous associations with resistance. Multivariate analysis found three independent factors associated with multidrug resistance: urinary catheter use (odds ratio [OR] 2.6, 95% confidence interval [CI] 1.4 to 4.8), age > or = 65 years (OR 3.0, 95% CI 1.7 to 5.4) and antibiotic use (OR 4.6, 95% CI 2.8 to 7.5). Diabetes was also a risk factor when patients with urinary catheters were excluded (OR 2.4, 95% CI 1.1 to 5.3). Resistance was seen in all groups of patients, but was particularly common in older patients and those who used a urinary catheter. Antibiotic use was highly associated with multidrug resistance.