Aspirin intolerance in patients with chronic sinusitis is often a cause of early recurrence of symptoms after surgical treatment. This study assesses 84 patients who were tested for acetylsalicylic acid intolerance after presenting with symptoms like chronic rhinosinusitis, sometimes bronchial asthma, coexisting allergies or a history of aspirin sensitivity. Nasal polyposis was found in a majority of cases, often recurrent after previous surgery. The levels of eicosanoids such as peptido-leukotrienes and prostaglandin E2 were analyzed in isolated blood cells and compared with a healthy control group. Aspirin-intolerant patients showed elevated basal levels of peptido-leukotrienes and reduced basal levels of prostaglandin E2. Test results were graded in a system ranging from positive (68%), signifying aspirin intolerance, to borderline (18%) and negative results (14%). After screening patients with clinical findings indicating a possible aspirin intolerance, the results of this investigation reveal a strong correlation between the clinical symptomatology and the in vitro parameters of eicosanoid levels in isolated blood cells, indicating the need to induce aspirin tolerance to reduce the risk of recurrent rhinosinusitis.