Our manuscript shows infestation of the different population (by age groups, and by sex) with endoparasites and ectoparasites from 1996 till 2010, through seasons (spring, summer, autumn, winter).Parasitological examinations which were done at "Public health Institute" of Osjecko-baranjska county, and which were done at total of 3667 patients, were the methods of direct parasitological diagnostic for proof of parasitic elements in clinical samples, and the methods of indirect parasitological diagnostic, serological examination for proof of antibodies to antigens in the serum of the patients or of the asymptomatic parasite carriers. Development of causers of the diseases (parasites) is depending on the season. Results of our researches were processed with statistical program called Statistica 8.0 (StatSoft. Inc 1984-2008). From statistical parameters arithmetic middle (x), standard deviation (s), and standard error of the arithmetic middle (sx), are shown. Testing of the significance of differences between independent samples was done with t-test (ANOVA), and is shown in the chart using the appropriate letters (a,b,c). Determined parameters of total infestation and endoparasitic infestation, and total infestation and ectoparasitic infestation show statistically significant difference on the risk level of 0.05 regardless of the age or the sex group of the population of Osjecko-baranjska county. Determined parameters of monitoring infestation (endoparasitosis and ectoparasitosis) have shown statistically significant difference on the risk level of 0.05.