Landslides and roadside slope failures result in road blockage, damage and recurrent economic losses in most mountain regions of the world. The situation is often exacerbated in developing countries where existing engineering geological and geotechnical information is frequently limited or unavailable. Case examples from Bhutan and Ethiopia are used to highlight the value of engineering geological assessments applied to the rehabilitation of low-cost roads in landslide-prone mountain areas. In both case examples the roads were severely affected by landslides, making large sections impassable. Only limited engineering geological assessments had been carried out prior to road construction, therefore only a few of these hazards had been identified during project feasibility study and design phases. Following these failures, engineering geological investigations were carried out to determine their causes and mechanisms using field mapping, supplemented in places by trial pit investigation, laboratory testing and stability analysis. The case examples demonstrate the value in carrying out timely and appropriately scaled engineering geological assessments as key contributions to the investigation, analysis and mitigation of these hazards. On the basis of the case examples described, engineering geological techniques are categorized into essential, desirable and useful as a guide to future assessments.