People with mental illnesses face the dilemma of whether to disclose or conceal their diagnosis, but this dilemma was scarcely researched. To gain in-depth understanding of this dilemma, we interviewed 29 individuals with mental illnesses: 16 with major depression/bipolar disorders and 13 with schizophrenia. Using a phenomenological design, we analyzed individuals’ experiences, decision-making processes, and views of gains and costs regarding concealment and disclosure of mental illness. We found that participants employed both positive and negative disclosure/concealment practices. Positive practices included enhancing personal recovery, community integration, and/or supporting others. Negative practices occurred in forced, uncontrolled situations. We also identified various influencing factors, including familial norms of sharing, accumulated experiences with disclosure, and ascribed meaning to diagnosis. Based on these findings, we deepen the understanding about decision-making processes and the consequences of disclosing or concealing mental illness. We discuss how these finding can help consumers explore potential benefits and disadvantages of mental illness disclosure/concealment occurrences.