Hip abductor muscle strength and function is negatively impacted by the presence of hip osteoarthritis (OA). This study aimed to quantify differences in hip abductor muscle volume, fatty infiltration and strength in a unilateral hip OA population when compared to a control group. Impact of radiographic severity of OA on these variables was also examined.Volumes of gluteus maximus (GMax), medius (GMed) minimus (GMin) and tensor fascia lata (TFL) was measured using MRI and muscle volume asymmetry between limbs was calculated. Fatty infiltrate within muscles was graded using the Goutallier classification system. Hip abduction and rotation strength was tested using a dynamometer. Differences between groups or limbs were analysed using t-tests and differences in fatty infiltration using non-parametric tests.A statistically significant decrease in muscle volume was identified in GMax (P < 0.01), GMed (P < 0.02) and GMin (P < 0.01) on the affected side in the OA group compared to both the contralateral side and the control group and differences were related to severity of OA. Hip abduction and internal rotation strength was reduced in the OA group. Increased levels of fatty infiltration were identified in the affected limbs of the OA group for GMax (P = 0.01) and GMin (P = 0.04).Gluteal muscle atrophy, increased gluteal fatty infiltration and hip strength deficits were evident in the affected hips of OA participants. Since severity of OA was related to the extent of atrophy and fatty deposits, rehabilitation programs targeting these muscles could reverse or halt the progression of these structural and functional deficits.