Non-attendance at mental health clinics is an international problem. A survey was conducted in the UK investigating communication methods used by staff to inform and remind patients about appointments. Increased number of communication methods used was associated with a reduced non-attendance rate. A care modelling analysis is provided that explores the healthcare use of three hypothetical patients following clinic non-attendance. The financial and environmental costs of each are then calculated and results discussed. Reducing non-attendance is achievable through the use of multiple communication methods. This small change can improve the sustainability of mental healthcare in different countries by improving quality of care and reducing financial and environmental costs.