We carried out a prospective study of 530 patients older than 14 years of age with brucellosis. We describe the incidence and clinical features of the focal forms of the disease, analyzing some of the possible factors associated with their appearance. One hundred sixty-nine patients (31.9%) had a focal form or complication. Osteoarticular complications were the most frequent, totaling 113 cases (66%), followed by genitourinary with 18 cases (5.1% of males), hepatic (2.5%), neurologic (1.7%), and heart (1.5%). Nine patients (1.7%) had more than 1 complication. In a multivariate analysis, diagnostic delay greater than 30 days (OR 2.0), ESR > 40 mm/hr (OR 1.9), and levels of alpha-2 globulin > 7.5 g/L (OR 6.8) were statistically significant independent variables associated with the presence of focal forms. Twenty-five patients with complications (14.8%) required surgical treatment. The relapse rate was 3.6% for those patients without complications and 4.1% for patients with focal forms (p > 0.05). However, when therapeutic failure, relapses, and mortality were considered together, the risk of an unfavorable evolution was significantly greater in patients with focal forms (10.6% versus 3.6% in patients without complications; OR 1.9, 95% CI 1.4-7.1, p < 0.005). Given the worse prognosis, knowledge and early diagnosis of the focal forms of B. melitensis infection is especially important.