The aim of this article was to summarize the evidence concerning the association between Mediterranean dietary pattern and cancer risk in observational epidemiological studies. All the studies that met the following criteria were reviewed: human cohort and case-control studies that examined the effect of the Mediterranean diet as an entire food pattern (the combined effect of individual components of the Mediterranean diet) and whose results were published in English. Out of the 12 reviewed studies (7 cohort and 5 case-control), 10 studies (6 cohort and 4 case-control) provided some evidence that the Mediterranean diet was associated with a reduced risk of cancer incidence or mortality. Although the reviewed studies varied according to certain study characteristics, such as being set in different populations and studying different cancer outcomes, the existing evidence from observational studies collectively suggests that there is a "probable" protective role of the Mediterranean diet toward cancer in general. Specific results for several outcomes such as different cancer sites deserve additional evidence. This favorable effect of the Mediterranean diet on cancer reduction is of public health relevance, given the tendency of modern societies to shift toward a more U.S. and Northern European dietary pattern.