Background: Safe alternatives to custody for offenders with mental disorder are vital, not least as self-harm, and violence rates are rising among them in prisons. In England and Wales, the Criminal Justice Act 2003 allows a mental health treatment requirement (MHTR) to supplement a community or suspended prison sentence, but this combination is poorly understood and rarely sought.Aim: To explore offenders' perspectives on the MHTR. Methods:We interviewed all 25 consenting offenders under an MHTR in two probation areas. Verbatim transcripts of their audio-taped narratives were analysed using grounded theory methods.Results: Their core concern was "instability," characterised by many health and social difficulties and resolved by achieving stability, which included not reoffending as well as becoming healthy, substance free, and "having a life." Most considered that the MHTR helped their motivation and service provision, but some cited poor supervisor accessibility, supervisor role confusion, and sense of stigma under the order as stressful and threatening good outcomes. Conclusions: This first account of offenders' perspectives on the MHTR suggests a model in which, under it, offenders see themselves making progress as courts require. They understand the risk of return to court and imprisonment if in breach. This model of understanding how MHTRs work could provide for professional guidance and evaluation of their effectiveness.