Background This study aimed to find markers to predict complicated cases in brucellosis. Patients with and without complications were compared in terms of epidemiological, clinical and laboratory properties. Methods A total of 700 patients hospitalised at the Department of Infectious Diseases and Clinical Microbiology were evaluated retrospectively. Results Of a total of 700 patients, 383 (54.7%) were male and mean age was 41.5 +/- 17.0 years. Of the patients, 517 (73.8%) were classified as acute cases. Complications occurred significantly less frequently in acute infections (p<0.001). Increased C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) occurred more frequently in patients with complicated cases (p=0.005 and 0.021, respectively), whereas malaise, myalgia and blood culture positivity occurred significantly less frequently in those cases (p<0.001, <0.001 and 0.014, respectively). Fever at examination, loss of malaise and myalgia and blood culture negativity were statistically significant predictive factors for complicated patients in multivariate analysis (p<0.001, for each). As compared to patients without orchitis, leukocytosis occurred more often in cases with orchitis (p<0.001); leukopenia occurred more often in neurobrucellosis than in cases without neurobrucellosis (p=0.008). Of patients who attended control regularly, 422 (98%) were treated successfully. All of the nine patients who did not recover fully were cases with osteoarticular involvement. Conclusions Fever was the most significant predictive marker of complications. Other classical symptoms of brucellosis like myalgia and malaise were absent in most of the complicated cases. Blood culture was of limited value in the diagnosis of complicated cases most of the time.