This paper is the report of a study to determine the effect on pain of internally rotating the foot, pointing the toes down and/or using the Z-track technique during intramuscular injection and to investigate differences in pain perception related to gender and body mass index. A randomized controlled trial was carried out from September to November 2010 on 75 patients receiving diclofenac sodium intramuscularly at a university hospital in Zonguldak, Turkey. The primary outcome measure collected was pain intensity, measured on a visual analogue scale. Each subject received three injections by the same investigator using three different techniques. The three techniques were randomly allocated, and the subjects were blinded to the injection technique being used. After each injection, another investigator, who had no prior knowledge of which injection technique was used, immediately assessed pain intensity using the visual analogue scale. Research findings demonstrated that the Z-track and internally rotated foot techniques significantly reduced pain intensity during intramuscular injection. Statistically significant differences in pain intensity were observed between the three injection techniques. The results supported the hypothesis that the internally rotated foot and Z-track techniques significantly reduce pain intensity.