Persuasive personal monitoring and feedback systems could help patients and clinicians manage mental illness. Mental illness is complex, difficult to treat, and carries social stigma. From a review of literature on bipolar disorder and interviews with bipolar disorder experts, we developed a framework for designing a persuasive monitoring system to support management of the illness. The framework applies a user-centered design process that is especially sensitive to the complexity of the illness, the difficulty of treatment, its stigma, and the goals of patients and clinicians. We describe our application of this framework to designing a persuasive mobile phone monitoring system. We discuss how our use of the framework can help overcome the special challenges posed by designing systems for mental illness: (1) accommodating a complex array of symptoms, (2) supporting an uncertain treatment process, and (3) maintaining a high level of sensitivity to the seriousness and darkness of the illness, as well as the social stigma associated with it.