This study examines the frequency and significance of diffuse liver uptake on 131I whole-body thyroid cancer scans. Sixty whole-body scans on 27 patients with differentiated thyroid cancer were reviewed. Liver uptake was quantitated on another 21 studies (16 patients). Diffuse hepatic uptake was seen in 44% of patients and 35% of all the studies. It correlated best with the 131I dose administered (r = 0.733) and the product of the 131I percent radioactive iodine uptake (RAIU) and administered dose (r = 0.656), less well with the serum 131I protein bound iodine (r = 0.494) and the RAIU. This study demonstrates that liver visualization is more common than generally appreciated and is related to the 131I dose and indices of thyroid function although other factors may also play a role in liver visualization.