Using MRI, we evaluated the degree of involvement of muscles in the lower extremities of 18 unselected patients with facioscapulohumeral muscular dystrophy (FSHD). Findings were correlated with fragment size of the mutated gene, age, disease duration and muscle power. Most affected muscles were the hamstrings followed by the tibialis anterior and the medial gastrocnemius. The vastus-, gluteal- and peroneal muscles were the most unaffected, and the psoas muscle did not show evidence of involvement in any of the investigated subjects. Asymmetric involvement was evident in 15% of the investigated muscles on MRI and 6% on manual muscle strength testing. MRI findings in muscle tended to correlate with disease duration (r = 0.49; p < 0.05), but not with gene fragment size or age. MRI disclosed involvement of muscles performing hip flexion and ankle dorsal flexion that could not be detected by manual muscle strength testing. Otherwise, there was a close correlation (approximately r = 0.75; p < 0.0001) between muscle strength and MRI severity score for other muscle groups. The present study shows that MRI may disclose muscle involvement in FSHD that is not apparent on manual muscle testing, and suggests that MRI of muscle may be an important assessment tool in clinical trials involving patients with FSHD.