Background: Toxoplasmosis is an opportunistic life threatening infection in immunocompromised patients caused by Toxoplasma gondii (T. gondii). Objectives: The present study was carried out to detect role of IgG avidity test in diagnosis of toxoplasmosis and distinguish between recent and old infection among immunocompromised patients and to detect risk of transmission of toxoplasmosis by blood donation. Methodology: This case control study was carried upon two groups, Group (1): 100 immunocompromised patients and Group (2): 100 individuals as immunocompetent control group. All serum samples were tested for anti-Toxoplasma (IgG, IgM) by Enzyme linked immunosorbent assay (ELISA) test. IgG avidity ELISA test was done to all cases with positive IgM, positive IgG or both. Results: Seroprevalence rate of anti-Toxoplasma IgM and IgG in immuncompromised group was 11% and 50% respectively which was higher than control group 4% and 32%. Results of IgG avidity test although ten cases (12.2%) were positive IgM and IgG, but they were old infection (avidity index (AI) was > 50%). Also two cases (2.44%) were positive IgM and IgG and they were recent infection (AI was <45%). Conclusion: Diagnosis of toxoplasmosis should not only relay on results of IgM and IgG ELISA test and must be combined with IgG avidity test as obligatory confirmatory step test for routine serological tests especially in those whom diagnosis of toxoplasmosis is critical as immunocompromised patients.