Purpose There are two main goals in hepatocellular carcinoma management, the first is long term survival and the second is the low recurrence rate after the treatment. Therefore, a lot of selection criteria defined for each treatment method and tumor size is one of the most important parameter in almost all of them. Methods In this review, importance of diamater in hepatocellular carcinoma is reviewed. Results Many reports showed a significant association between increase in maximum tumor diameter and microvascular invasion. Patients with larger tumors are more likely to have poorly differentiated tumors. Increased regional and distant metastasis of tumors were observed in the larger size hepatocellular carcinoma. Liver transplantation represents the best treatment option for patients with decompensated liver cirrhosis and hepatocellular carcinoma. Conclusions Combined with biological, inflammatory, radiological, pathological and genetic markers that predict the biological behavior of the tumor, today, tumor size is one of the best aggressiveness markers until new markers are found. So, tumor size is matter.