To estimate the healthcare utilization and costs of major diabetes mellitus (DM)-related complications in Taiwan in the year of first occurrence and in subsequent years.This study is a retrospective claim database analysis using the longitudinal cohort of diabetes patients (LHDB) with 2012 as the base year. Occurrences of 8 DM-related complications of interest were identified using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. Annual healthcare costs and utilization of these DM-related complications in the LHDB cohorts of the years 2004 to 2009 were examined, and the generalized linear model was used to estimate annual total healthcare costs for each complication.DM patients with complications were more likely to have at least 1 emergency room (ER) visit and at least 1 hospitalization (both P < .001), and they also had more outpatient visits, higher hospitalization costs, higher outpatient costs, and higher ER costs (all P < .001) than those without. The mean annual total healthcare cost of the patients with DM-related complications was US $4189, whereas the mean annual cost of those patients without complication was $1424 (P < .001). The complications with the greatest event costs were amputation ($7877; 95% confidence interval [CI]: $6628-$9322) and fatal MI ($4067; 95% CI: $3001-$5396) while the complication with the greatest state costs was end-stage renal disease (ESRD) ($2228; 95% CI: $2155 to $2302).DM-related complications could significantly increase healthcare utilization and costs. The results of this study provide data that are useful for local economic evaluations of DM treatments.