Objectives Long-term metformin is associated with vitamin B12 deficiency. There is a significant misunderstanding among both physicians and patients regarding vitamin B12 indications. This study aims to identify knowledge gaps and attitudes towardvitamin B12 among diabetic patients. Materials and methods A cross-sectional study was conducted among type 2 diabetic patients visiting four primary healthcare centers in Buraidah, Saudi Arabia. The data were collected using a structured self-administeredquestionnaire. Data were collected on diabetes and vitamin B12 knowledge and attitude towardvitaminB12 supplementation.Logistic regression analyses were used to assess the predictors of knowledge and attitude. Results Of the 388 participants, 192 (49.5%) were male. About 84.5% of the total diabetics were on metformin. Nearly three-fourths (72.7%) were taking vitamin B12. A large proportion, 160 (41.2%), believed that it is necessary to take vitamin B12 for every diabetic patient. Nearly half, 193 (49.7%), did not know the factors affecting vitamin B12 deficiency. Young (less than 39 years) diabetics were more likely to perceive that vitamin B12 is recommended for all diabetics, OR (95% CI) [6.26 (1.86-21.06)], as compared to participants aged more than 59. Similarly, younger patients were more likely to assume vitamin B12 necessary, OR (95% CI) [3.71 (1.26-10.89)]. Conclusion We found the knowledge and attitude of diabetic patients regarding vitamin B12 to be poor. It is, therefore, recommended that primary health care providers educate their patients about vitamin B12 supplementation to reduce the number of medications and financial burden. Further large-scale studies are also needed to generate stronger evidence of the problem.