Blastocystis hominis can be found in the fecal sample of both healthy individuals without symptoms and those having gastrointestinal problems. Therefore, the pathogenicity and pathophysiology remain controversial. The aim of this study was to determine if Blastocystis hominis is a causative agent of diarrhea and investigates its prevalence among patients visiting King Abdulaziz University Hospital, Jeddah, Saudi Arabia from January 2013 till June 2015 and to determine any significant correlation between age, gender, nationality and other parasitic infection in the presence of Blastocystis hominis. Data were collected from Parasitology lab, using the database at King Abdulaziz University Hospital, Jeddah, Saudi Arabia and statistical analysis were done by utilizing Statistical package for social science program (SPSS). Out of 3,035 of total stool analysis requested, 157 samples were positive for B. hominis (5.2%). 80 (51.6%) were males, and 76 (48.4%) were females. The distribution of B. hominis infection was elevated in 31-50 aged groups (25.5%). There was a statistically significant correlation between the presence of Blastocystis and diarrhea at p < 0.05 and there was no correlation between age, sex, nationality and other parasites with positivity of B. hominis. Blastocystis can be considered as a causative agent of diarrhea. Further studies need to be done in order to investigate its role in pathogenicity and more data must be revised to assess the pathogenicity of Blastocystis subtypes
