Environmental factors play an important role in the pathogenesis of type 1 diabetes and can determine if a genetically susceptible individual develops the disease. Increasing evidence suggest that among other exogenous agents certain virus infections can contribute to the beta-cell damaging process. Possible viral etiology of type 1 diabetes has been explored extensively but the final proof for causality is still lacking. Currently, the group of enteroviruses (EVs) is considered as the strongest candidate. These viruses have been found in the pancreas of type 1 diabetic patients, and epidemiological studies have shown more EV infections in diabetic patients than in controls. Prospective studies, such as the Type 1 Diabetes Prediction and Prevention (DIPP) study in Finland, are of fundamental importance in the evaluation viral effects as they can cover all stages of the beta-cell damaging process, including those preceding the initiation of the process. DIPP study has carried out the most comprehensive virological analyses ever done in prospective cohorts. This article summarizes the findings from these analyses and discuss them in the context of the existing other knowledge and the prospects for intervention studies with EV vaccines or antiviral drugs.