This paper considers impact assessment (IA) for a specific microfinance organisation working in an uncertain environment. It argues that there are significant learning points both for new clients and for the organisations who supply their services and products, which can result in improved, more targeted service provision. The paper is divided into two parts. The first part argues that improved capacity to assess the impact of services is a necessary element of the transition of many microfinance organisations (MFOs) from externally-funded clones to autonomous, flexible and competitive businesses. The second part explores impact assessment design by discussing the need to achieve a balance in choice of goals, data collection, data analysis, choice of indicators and staffing.