The objective of this study was to assess the discriminative properties of the methods for diagnosing acute maxillary sinusitis (AMS) in unselected patients. The study design was a systematic review of evaluation studies identified by using Medline, by searching reference lists, by hand searches, and by contacting investigators. Evaluation studies were conducted anywhere in the world. Subjects were adults with suspected AMS. Main outcome measures were: sensitivity, specificity, positive and negative likelihood ratios of the primary studies, weighted means of these parameters in each comparison (clinical examination, radiography, and ultrasound compared to a reference standard in diagnosing AMS), and summary ROC curves and their Q* points where sensitivity equals specificity. For the years from 1962 to present, 49 study reports were found; 11 articles on studies that included a total of 1144 patients were eligible. Compared to sinus puncture, radiography was the most accurate method for diagnosing AMS: the Q* point on the summary ROC curve was 0.82 (95% confidence interval, CI, 0.78-0.85). Ultrasound was slightly less accurate than radiography compared to sinus puncture (Q* 0.80, 95% CI 0.76-0.83). Only two articles reported clinical examination compared to sinus puncture and the Q* for them was 0.75 (95% 0.58-0.86). Clinical examination is a rather unreliable method for diagnosing AMS, even in the hands of experienced specialists. Using radiography or ultrasound improves the accuracy of diagnosis. The diagnosis of AMS is rarely studied in primary care settings. Future comparative trials should preferably combine diagnosis and treatment, evaluating the two aspects of clinical management as unit.