For the past two decades or more, obesity has been increasing in industrialized and affluent countries. This increase has been shown in children, adults and the elderly. The latest statistical studies in Saudi Arabia show that obesity is increasing, with obese Saudi women outnumbering obese Saudi males, and that these numbers are continuously rising. Obesity, which leads to many medical risks, affects the immune system in direct and indirect ways. In this study, the effect of obesity on the immune system of 119 Saudi female university students was investigated. Using a blood sample from each subject, the following immune-related parameters were determined: total and differential white blood cell counts (WBCs), total lymphocyte and sub-lymphocyte cell counts. Two measures of body fat were used: the body mass index (BMI) and the waist-to-hip ratio (WHR) to correlate body weight to the other measured parameters. A significant correlation was present between BMI and WHR each with total white blood cells, neutrophils, and CD4 lymphocyte concentrations. Some other parameters were only affected by the increase in the BMI but not the WHR, such as platelets, while others were affected by the WHR only, such as total T-cells. On the other hand, there were no significant correlations between BMI or WHR and basophil, eosinophil, monocyte, CD8, B-cell, and NK-cell counts. The findings indicate that obesity might seriously affect the innate and adaptive immune systems.