OBJECTIVE We aimed in this paper to investigate some immunohematological characteristics of Nigerian sickle cell anemia (SCA) patients with osteomyelitis. METHODS Thirty SCA patients with osteomyelitis (SO) and 30 SCA patients without osteomyelitis (S) were investigated. The PCV, WBC and platelet count were done on automated counter, while the erytorocyte sedimentation rate (ESR) was determined by Westergren's technique. C3 activator, C1-INH, IgA, IgG and IgM were estimated by the single radial immunodiffusion method. RESULTS The SO patients weighed less (z =1.943, p<0.055) and were shorter (z = -2.064, p<0.039). High serum levels of IgG, IgM, C1-INH and C3 activator were also found in the SO group. ESR correlated positively with hematocrit (r=0.371, p<0.04) and C3 activator (r=0.468, p<0.03) in SO. Similarly, WBC correlated positively with C1-INH (r=0.806, p<0.01), while we also noted positive correlation between C1-INH and C3 activator (r=0.525, p<0.02). In SO, ESR correlated positively with both IgM (r=0.531, p<0.02) and C3 activator (r=0.449, p<0.05). CONCLUSIONS This study suggests some derangement in immune status in Nigerian SCA patients with osteomyelitis and that C1-INH and C3 activator may be useful markers of immune status in SCA patients.