Small (less than 5 cm) hepatocellular carcinomas (HCCs) in 45 of 112 patients (40.2%) had a high-signal-intensity pattern (relative to that of liver) on T1-weighted magnetic resonance (MR) images. To identify the cause of this pattern, specimens of histologically defined HCC with high- (n = 21), iso- (n = 6), and low- (n = 22) intensity patterns were histologically evaluated for paramagnetic ionic forms of metals. The incidence of steatosis, clear cell formation, and copper accumulation was statistically (P less than .01) higher in tumors with the high-intensity pattern than in those with other patterns. Of 17 HCCs that stained positive for copper, 16 (94%) had a high-intensity pattern; the pattern of one tumor (6%) was isointense. All 21 tumors with the high-intensity pattern had at least one of the findings of steatosis, clear cell formation, or copper accumulation. These features were evident in only four of 28 tumors (14%) with an iso- or low-intensity pattern. Thus, copper accumulation might be a cause of the high-intensity pattern on T1-weighted images of small HCCs.