Background: Diabetes mellitus (DM) is considered to be a risk factor in the prognosis of many types of cancer, but the effect of DM on the risk of non-Hodgkin lymphoma (NHL) is still under dispute. We performed this study to examine the association between DM and subsequent NHL risk. Methods: A systematically search had been performed in PubMed, EmBase, and the Cochrane Library to identify eligible studies from inception to September 2018. Results: Thirteen cohort studies were included, with a total of 9024761 participants. The results showed that DM was associated with an increased risk of NHL (RR = 1.15, 95%CI: 1.02, 1.30, P = .03). Subgroup analyses suggested that DM was significantly associated with patients aged less than 60 years old (RR = 1.65, 95%CI: 1.31, 2.09, P < .0001), follow-up duration within 8 years (RR = 1.23, 95%CI: 1.02, 1.48, P = .03), and studies adjusted for body mass index (RR = 1.35, 95%CI: 1.01, 1.79, P = .04). The analyses within DM patients indicated that DM men were more likely to develop NHL than DM women (RR = 1.31, 95%CI: 1.04, 1.65, P = .02). Conclusions: These results indicated that DM patients have significantly increased risk of NHL compared nondiabetics. Male DM patients were more likely to develop NHL compared with female. However, further large-scale studies are required to eliminate miscellaneous factors in all included studies.