To determine the tumor size that constitutes early pancreatic cancer, we reviewed and analyzed the English-language and Japanese literature (a total of 25 publications) on small pancreatic cancers less than 2 cm in diameter and/or stage 1 cancers. Reports on in situ carcinoma and intraductal carcinoma of the pancreas were also evaluated. The results were: (1) A total of 302 cases of small pancreatic cancer less than 2 cm in diameter reported at separate institutions were pooled from 15 reports. The rates for patients in stage I and those with no lymph node metastasis averaged 41.7% and 57.9%, respectively. The 5-year postoperative cumulative survival rate (5Y-PCR) was less than 50% in almost all these reports. Similar data were shown in the 7 collective reviews. (2) Another 33 cases of small pancreatic cancer of 1 cm or less in diameter were collected from three reports. The rates for stage I tumor and 5Y-PCR at one institution with two reports were 100% and 100% and the rates in the other report were 85% and 78%, respectively. (3) Twelve cases of in situ carcinoma and intraductal carcinoma of the pancreas were collected from four reports. All of the patients were stage I and were alive with no evidence of tumor recurrence for periods ranging from 6 to 78 months. Small pancreatic cancer less than 1 cm in diameter is better viewed as an early pancreatic cancer, and in situ carcinoma and intraductal carcinoma of the pancreas with minimal invasion to the pancreatic parenchyma may be defined as early pancreatic cancer, regardless of size.