For the rational treatment of sinusitis, it is essential to distinguish sinusitis of bacterial origin from that of other etiologies. In maxillary sinusitis, antral purulence indicates a significant amount of pathogenic bacteria, whereas the presence of bacteria seems to be of less or no relevance in nonpurulent sinusitis. Hence, from a therapeutic point of view one important diagnostic goal is the differentiation of purulent from nonpurulent sinusitis. In this respect clinical examination is fairly reliable. Sinus radiography cannot distinguish purulent from nonpurulent sinusitis and offers few advantages when deciding on antibiotic therapy. Antral aspiration offers the most comprehensive information on which to base a reliable diagnosis.