The use of magnetic resonance imaging (MRI) has modified the imaging strategies of inflammatory arthritides. In psoriatic arthritis (PsA), MRI study of the nail unit identifies nail involvement that appears as the initial lesion for induction of distal phalanx damage and consequently of distal interphalangeal joint arthritis. All psoriatic patients, also in the absence of a clinically evident onychopathy, show characteristic MRI changes of the nail. This evidence could have practical diagnostic value because MRI study of the nail could document diagnosis in patients with undifferentiated spondyloarthropathies who have barely evident psoriasis. We discuss the advantages and problems related to the use of low- and high-field MRI in the study of the nail unit of patients with PsA.