Objective: To examine the effects of sociodemographic characteristics, health status, comorbidity, provider, medication and financial variables on insulin initiation behavior for type 2 diabetics on multiple oral antidiabetic medications. Methods: The 2002-2006 MarketScan Research Databases were used to study the health care utilization and expenditure patterns of adults with type 2 diabetes in employer-sponsored health plans in the United States. The utilization patterns of 38,768 patients with Type 2 diabetes who were adherent to one oral antidiabetic medication and added a second oral medication for at least 6 months were analyzed. Two outcomes were examined: insulin initiation within 12 months and the amount of time to insulin initiation. Multivariate logistic models were used to estimate the effects of the explanatory variables on the likelihood of insulin initiation. Cox proportional hazard models with prescription drug and office visit copayments as time-varying covariates were used to estimate the effects of the explanatory variables on the amount of time to insulin initiation. Results: A total of 16.5% of patients initiated insulin within one year. A variety of determinants were associated with insulin initiation within a year: age (Adjusted Odds Ratio 0.982, 95% CI (0.980, 0.985) ), health status indicated by the presence of factors such as heart disease (AOR 1.48 (1.317, 1.654)), myocardial infarction (AOR 1.32, (1.068, 1.640)), diabetic retinopathy (AOR 1.26, (1.120, 1.406)), the number of nondiabetes medications (AOR 1.03, (1.030, 1.039)), and insulin copayments (AOR 0.998, (0.995, 1.000)). The amount of time to insulin initiation was also affected by similar factors. Conclusion: Health status appears to be the strongest predictor of insulin initiation in patients initiating insulin for type 2 diabetics who are adherent to oral medications. Providers, health plans and employers should be aware of the factors that influence the addition of a medication to a treatment regimen for chronically-ill patients.