Mastitis is an endemic disease that is considered to be one of the most frequent and costly dairy disease, so the aim of this study was to investigate different factors that affecting mastitis incidence, and their effect on productivity and profitability of dairy farms. Data used in this study were estimated from 1353 lactation records of Friesian dairy cows within private and governmental farms. The productive, reproductive and economic data for a whole lactation season were recorded for healthy and mastitic cows. Four risk factors for mastitis were included (production sector, calving season, parity and milk production level). Data were classified according to risk factors into two production sectors private and governmental, two calving seasons, summer and winter and Six lactation orders from 1stto 6th, two milk production levels (high and low milk producing cows). Winter calving, older and high producing cows and private sector had the highest mastitis incidence, mastitis reduced the 305MY of Mastitic cows by 33.7 & 20.3Kg during disease period, and 62.7 & 37.7Kg milk was discarded during treatment period for private and governmental sector respectively. Finally economic losses of mastitis per animal was 695.7 EGP yearly.