The sinusitis is the term, which describes inflammation process of mucous membrane of these sinuses. Generally inflammation spreads from the nose to the paranasal sinus, so rhinosinusitis is the common name of disease. In classification of sinusitis two aspects are important--duration of signs and symptoms and changes in mucous membrane of sinus. In acute sinusitis symptoms withdraw after treatment, and mucous membrane comes back to the normal state. The most frequent bacteria's responsible for sinusitis are aerobes and among them: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrrhalis, Streptococcus gr. A, Staphylococcus aureus, bacteria Gram (-) as well as anaerobic bacteria's. The inflammation changes of paranasal sinuses the most often enter on frontal ethmoid sinuses and then in frontal sinus, posterior ethmoid sinuses and the most seldom in sphenoid sinus. The diagnostics of sinusitis consisted of history data, otolaryngological examination, image diagnostics, bacteriological investigation, allergological diagnostics, sometimes alternatively, dentist as well as neurologist's consultations. The treatment of acute sinusitis is conservative. The aim of the treatment is control of inflammation, decrease of tissue oedema, facilitation of outflow of secretions of the nose and paranasal sinuses. We apply the antibiotics, glycocorticosteroids, decongestant drugs and mucolytic drugs. One should remember, that not treated or wrongly treated acute sinusitis can lead to chronic sinusitis or to numerous complications.