BACKGROUND Computed tomography (CT) scans are being utilized to examine the influence of skeletal muscle and visceral adipose quantity and quality on health-related outcomes in clinical populations. However, little is known about the influence of contrast administration on these parameters. METHODS Precontrast, arterial, and 3-minute postcontrast CT images of 45 patients with clear cell renal cell carcinoma were downloaded from The Cancer Imaging Archive and retrospectively analyzed for visceral adipose cross-sectional area (CSA) and density, and muscle CSA and density at the third lumbar vertebrae. Low muscle CSA index was defined as ≤38.9 cm /m for women and ≤55.4 cm /m for men. Low muscle density was defined as <41 Hounsfield units (HU) for body mass index (BMI) <24.9 kg/m and <33 HU for BMI ≥25.0 kg/m . RESULTS In both the arterial and 3-minute phases, contrast administration decreased visceral adipose CSA (-20.9 and -20.9 cm ; P < .001) and increased visceral adipose density (4.8 and 5.8 HU; P < .001), relative to precontrast images. Muscle CSA index marginally increased in the arterial (0.6 cm /m ; P = .007) and 3-minute phases (0.8 cm /m ; P < .001). This likely represents clinically insignificant changes because it does not alter the identification of low muscle CSA (44.4% vs 42.2%; P = 1.00). Skeletal muscle density increased in the arterial (6.4 HU; P < .001) and 3-minute phases (8.7 HU; P < .001), which altered the identification of low muscle density (6.7% vs 31.1%; P < .001). CONCLUSIONS Future analyses should consider the phase of contrast during CT imaging because it may alter the interpretations of several parameters.