Recent reports in the surgical literature state that persistent dense visualization of an otherwise normal-appearing gallbladder 36 hr after the administration of iopanoic acid is highly suggestive of acalculous cholecystitis. To determine the incidence and significance of persistent gallbladder visualization, 324 patients and 66 asymptomatic controls were evaluated. An equal percentage (about 10%) of both groups showed persistent dense gallbladder opacification 36 hr after iopanoic acid ingestion. The results do not support the contention that patients with acalculous cholecystitis can be identified by simply obtaining an additional abdominal radiograph the day after oral cholecystography.