Children living in families with parental substance abuse are at high risk of child maltreatment and associated adverse outcomes. A trial of methadone-maintained parents randomised to the Parents under Pressure (PuP) parenting programme reported significant improvements in family functioning relative to standard care or a brief intervention, as indicated by a reduction in scores on the Child Abuse Potential Inventory. We sought to determine the cost-effectiveness of the PuP programme to inform policy and programme implementation. The cost per expected case of child maltreatment prevented was calculated and compared with the estimated lifetime costs of maltreatment and sensitivity analyses were conducted. Compared to usual care, the PuP programme costs an additional AU$8777 (£4880) per family to deliver. Assuming the most conservative estimate of one in five cases of maltreatment prevented, a cost-effectiveness estimate of AU$43 975 (£24 451) per case of potential maltreatment prevented for the PuP group was obtained. This is significantly less than the estimated mean lifetime cost of a case of child maltreatment of AU$200 000 (2013 present value) (£110 000). For 100 families in this population treated with PuP, there would be a net present value saving of an estimated AU$3.1 million (£1.7 million). Copyright © 2015 John Wiley & Sons, Ltd.