OBJECTIVE The purposes of this study were to evaluate the effectiveness of radiologic studies in diagnosing sinusitis in the intensive care unit (ICU) patient and to compare it with the effectiveness of endoscopic examination of the middle meatus. METHODS We conducted a prospective collection of data in 141 ICU patients consulted for sinusitis over a 5-year period beginning in the 1994. RESULTS Antral lavage was performed at least unilaterally in 112 patients, with a total of 195 lavages performed. Plain films and computer tomography scans predicted purulence in 41% (chi(2) = 2.9, P = 0.09) and 47% (chi(2) = 2.2, P = 0.14) of the cases, respectively, whereas the presence of purulence in the middle meatus as seen on endoscopy predicted purulence in the maxillary sinus in 78% of the lavages (chi(2) = 28.9, P = 8 x 10(-8)). When there was no evidence of purulence in the middle meatus on endoscopy, 73% of the lavages were negative. CONCLUSIONS The most important predictor of a positive antral lavage in the ICU patient with suspected sinusitis is evidence of purulence on endoscopic examination of the middle meatus.