Objective: To evaluate the association between the type of information source and the level of knowledge about diabetes mellitus in patients with type 2 diabetes. Methodology: A cross-sectional study was conducted at a reference diabetes and hypertension center in Lima, Peru, during 2014. Level of knowledge was measured using the Diabetes Knowledge Questionnaire-24 and 12 information sources. Patients with 75% correct answers were considered to have a good knowledge. Adjusted odds ratios were calculated. Results: Of the total 464 patients enrolled, 52.2% were females, and 20.3% used the Internet as information source. Mean knowledge was 12.9 ± 4.8, and only 17.0% had a good knowledge, which was associated with information on diabetes obtained from the Internet (OR = 2.03, 95% CI 1.32 to 3.14), and also from other patients (OR = 1.99, 95% CI 1.20 to 3.31). Good knowledge was also associated with postgraduate education (OR = 3.66, 95% CI 1.21 to 11.09), disease duration longer than 12 years (OR = 1.91, 95% CI 1,22 to 3.01), and age older than 70 years (OR = 0.39, 95% CI 0.21-0.72). Conclusion: Search for information in the Internet was positively associated to a good level of knowledge. It is suggested to teach patients with diabetes to seek information on the Internet and, on the other hand, to develop virtual spaces for interaction of patients with diabetes.