Treatment adherence is of critical importance in the management of patients with IBD. Poor adherence can lead to increased disease activity, loss of response to therapy, and increased costs of care. It has been well established that adherence to long-term therapy for chronic illnesses is extremely poor, averaging around 50% in developed countries. Measured rates of nonadherence in IBD are similar, but vary depending on the type of therapy and the population being observed. This article reviews the scientific data on treatment nonadherence in IBD. The methods commonly used to evaluate treatment adherence investigation are reviewed. The consequences and scope of treatment nonadherence are summarized. Finally, the scientific data on management strategies to address the problem of treatment nonadherence are explored.