Intraductal papillary mucinous neoplasms (IPMNs) show varying degrees of dysplasia throughout the neoplasm that can range from adenoma to invasive carcinoma, with dysplastic changes of borderline neoplasms and carcinoma in situ in between. An understanding of the natural history, and especially the required time to transform into either carcinoma in situ or an invasive adenocarcinoma, is critically important for management policy. This topic serves as the rationale for the present analysis. At the beginning of February 2007, using the key word "IPMN" in PubMed, we initially selected 119 publications using the principal criteria as defined by the WHO classification. We identified 20 appropriate original reports and one consensus paper. Neither randomized control trials (RCT) or systematic reviews of RCTs (level 1 evidence) nor cohort studies or reviews of cohort studies (level 2 evidence) have been published. Only one report fit the criteria for level 3 evidence (case control study). Nineteen papers satisfied criteria for level 4 (cases series) and two for level 5 (expert opinion publication). After additional review and analysis, we considered only six reports to be "cornerstone papers" of merit for the final review. Clues to the natural history of IPMNs can be gained by using several methods to examine the articles: (a) to verify different prognoses between main and side branch duct subtypes; (b) to compare the average age of patients with benign vs. malignant IPMNs; (c) to summarize the findings of nonoperative, observational studies based on follow up by clinical, biochemical, and imaging techniques without operative resection; (d) to determine the prognostic importance of the status of the resection margin; and (e) to follow patients clinically after surgical resection. Although important aspects of the natural history of IPMN are still unknown, the following conclusions can be drawn: (1) Branch-duct IPMNs are less aggressive than main-duct IPMNs. (2) Malignancy is more common in older patients. (3) Malignancy (invasive or carcinoma in situ) is found in about 70% of resected main-duct IPMNs. (4) After resection of noninvasive IPMNs (branch- and main-duct varieties), recurrence is rare (<8%). (5) After resection of invasive IPMN, recurrence occurs in 50-65% of patients.