OBJECTIVES: This retrospective cohort study aimed to examine the association between hypoglycemia and medication adherence among veterans with type 2 diabetes mellitus (T2DM) in the United States. METHODS: Electronic medical and pharmacy records were obtained for patients with at least 2 records of T2DM diagnosis (ICD-9-CM codes: 250.xx except for 250.x1 and 250.x3) from the Veterans Integrated Service Network (VISN) 16 data warehouse from January 1, 2004 to September 1, 2010. The VISN 16 serves veterans in Arkansas, Louisiana, Mississippi, Oklahoma, and parts of Alabama, Florida, Missouri, and Texas.  The first dispense date of a new antihyperglycemic agent (index drug) was defined as the index date.  The hypoglycemia and control cohorts were identified by the occurrence of hypoglycemia (ICD-9-CM codes: 250.8, 251.0, 251.1 and 251.2) during the index-treatment period and no hypoglycemia during one-year post-index period, respectively.  Selected patients had no records of hypoglycemia, cardio-vascular disease, or micro-vascular complications during the one-year pre-index period.  Selection bias across cohorts was reduced using propensity score matching. The medication possession ratio (MPR) and proportion of MPR>=80% of the index drug and overall anti-hyperglycemic medications were used as indicators for medication adherence.  Generalized linear model and logistic regression model were used to compare MPR and proportion of MPR>=80% between the two groups, respectively. RESULTS: The 761 patients in the hypoglycemia group were matched with 761 patients from the control group of 43,500 patients.  As to the index drug, MPR was slightly higher in the hypoglycemia group (0.66 vs. 0.63; p=0.009), but  proportion of MPR>=80% did not significantly differ between the groups (hypoglycemia: 38.44% versus control: 36.06%; p=0.3387), controlling for the covariates.  Also no differences in MPR and proportion of MPR>=80% to overall antihyperglycemics were found between the groups. CONCLUSIONS:  It appears that there is little impact of hypoglycemic event during treatment on the MPR statistics in this population.