Purpose: To study the thickness of gluteal subcutaneous fat (SCF) and propose an adequate length for needle for gluteal intramuscular injections based on computed tomography (CT) measurements. Methods: The thickness of gluteal SCF were measured and studied for 568 patients who visited a tertiary hospital in Seoul, Korea between January 2007 and February 2009 for routine health screening and who had abdominopelvic CT. Results: The average thickness of gluteal SCF was $15.92{pm}4.08mm$ in males and $24.90{pm}5.47mm$ in females. The thickness of gluteal SCF differed significantly according to gender. The gluteal SCF thickness was greater than 20.4 mm for 54 (12.3%) of the 440 male patients and 99 (77.3%) of the 128 female patients. Conclusion: The most common syringe needle used for gluteal intramuscular injections in Korea is a 23 G, 25.4 mm-needle. The SCF thickness must be less than 20.4 mm in order to reach the dorsogluteal muscles to a depth of at least 5 mm if this 25.4 mm needle is used. In many patients, especially in female patients, the 25.4 mm needles will result in improper intramuscular injections with the injection being into the SCF. Therefore an appropriate needle should be selected by considering the gender and SCF thickness of patients receiving gluteal intramuscular injections.