We identified 43 512 KPNC members with an incident diagno- sis of vitamin B12 deficiency between January 1, 1997, and June 30, 2011. We excluded case patients lacking matched controls (n = 234), potential cases (n = 1751) and controls with diagno- ses known to directly cause vitamin B12 deficiency, and po- tential cases (15 571) and controls who had taken PPIs or H2RAs for less than 2 years. This resulted in 25 956 cases and 184 199 controls in the final analyses. Case patients were predomi- nantly female (57.4%), 60 years or older (67.2%), and of non- Hispanic white race/ethnicity (68.4%) (Table 1).