The aim of the investigation was to study the efficiency of positron emission tomography with [¹⁸F]-fluorodeoxyglucose in diagnosis of various bronchopulmonary diseases taking into account the mass size of a pathological formation and the level of metabolic activity. A retrospective analysis of 615 patients with focal or infiltrative changes in the lungs was performed. The maximum level of Standardized Uptake Value (SUV) was measured in 443 of 615 patients with focal glucose hypermetabolism uptake. There was proposed the new method of calculating the SUV threshold depending on the size of the pathological formation. On the basis of the size of the pathological formation the new method of SUV threshold calculating was proposed depending on the mass size. Sensitivity, specificity, positive and negative predictive values of the method were calculated taking into account the mass size. The greatest number of false-positive and false-negative results was obtained in the SUV range from 1.9 to 4.3. The optimal SUV threshold for lung cancer revelation was defined by trees classification method.