Introduction. Odontogenic maxillary sinusitis (OMS) is an inflammatory disease caused by the spread of dental inflammation into the sinus. The rate of OMS was reported to be 25-40%. A lot of methods of treatment were proposed starting with medicine administration only, till radical sinusotomy. The question is what is the efficacy of the initial treatment, the one that includes the treatment of causal tooth only.  Aim of the study. The purpose of this study was to identify the factors of significance that may contribute to the results of the initial treatment of OMS.   Materials and methods. Twenty four patients were studied, which were divided in 2 groups, depending on the result of the treatment: effective and non-effective. Efficacy of the treatment was evaluated 3 months after causative tooth treatment with CT scan, which was compared with initial one. First group included 21 patients and the second one 3 persons, that required surgical treatment.  Conclusions. 1. Causal tooth treatment of OMS is an effective and miniinvasive method.  2. Maxillary ostium obstruction is an important factor to predict outcome of the treatment