Older patients with diabetes mellitus receiving medical treatment whose blood pressure (BP) or blood glucose level are potentially dangerously low are rarely deintensified. Given the established risks of low blood pressure and blood glucose, this is a major opportunity to decrease medication harm.To examine the rate of BP- and blood glucose-lowering medicine deintensification among older patients with type 1 or 2 diabetes mellitus who potentially receive overtreatment.Retrospective cohort study conducted using data from the US Veterans Health Administration. Participants included 211 667 patients older than 70 years with diabetes mellitus who were receiving active treatment (defined as BP-lowering medications other than angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, or glucose-lowering medications other than metformin hydrochloride) from January 1 to December 31, 2012. Data analysis was performed December 10, 2013, to July 20, 2015.Participants were eligible for deintensification of treatment if they had low BP or a low hemoglobin A1c (HbA1c) level in their last measurement in 2012. We defined very low BP as less than 120/65 mm Hg, moderately low as systolic BP of 120 to 129 mm Hg or diastolic BP (DBP) less than 65 mm Hg, very low HbA1c as less than 6.0%, and moderately low HbA1c as 6.0% to 6.4%. All other values were not considered low.Medication deintensification, defined as discontinuation or dosage decrease within 6 months after the index measurement.The actively treated BP cohort included 211,667 participants, more than half of whom had moderately or very low BP levels. Of 104,486 patients with BP levels that were not low, treatment in 15.1% was deintensified. Of 25,955 patients with moderately low BP levels, treatment in 16.0% was deintensified. Among 81,226 patients with very low BP levels, 18.8% underwent BP medication deintensification. Of patients with very low BP levels whose treatment was not deintensified, only 0.2% had a follow-up BP measurement that was elevated (BP ≥140/90 mm Hg). The actively treated HbA1c cohort included 179,991 participants. Of 143,305 patients with HbA1c levels that were not low, treatment in 17.5% was deintensified. Of 23,769 patients with moderately low HbA1c levels, treatment in 20.9% was deintensified. Among 12,917 patients with very low HbA1c levels, 27.0% underwent medication deintensification. Of patients with very low HbA1c levels whose treatment was not deintensified, fewer than 0.8% had a follow-up HbA1c measurement that was elevated (≥7.5%).Among older patients whose treatment resulted in very low levels of HbA1c or BP, 27% or fewer underwent deintensification, representing a lost opportunity to reduce overtreatment. Low HbA1c or BP values or low life expectancy had little association with deintensification events. Practice guidelines and performance measures should place more focus on reducing overtreatment through deintensification.