Background/Aim: This paper reviews ecological studies of the ultraviolet-B (UVB)–vitamin D–cancer hypothesis based on geographical variation of cancer incidence and/or mortality rates. Materials and Methods: The review is based largely on three ecological studies of cancer rates from the United States; one each from Australia, China, France, Japan, and Spain; and eight multicountry, multifactorial studies of cancer incidence rates from more than 100 countries. Results: This review consistently found strong inverse correlations with solar UVB for 15 types of cancer: bladder, breast, cervical, colon, endometrial, esophageal, gastric, lung, ovarian, pancreatic, rectal, renal, and vulvar cancer; and Hodgkin’s and non-Hodgkin’s lymphoma. Weaker evidence exists for nine other types of cancer: brain, gallbladder, laryngeal, oral/pharyngeal, prostate, and thyroid cancer; leukemia; melanoma; and multiple myeloma. Conclusion: The evidence for the UVB–vitamin D–cancer hypothesis is very strong in general and for many types of cancer in particular.