This paper presents the first published report of a national-level effort to implement the integrated management of childhood illness (IMCI) strategy at scale. IMCI was introduced in Peru in late 1996, the early implementation phase started in 1997, with the expansion phase starting in 1998. Here we report on a retrospective evaluation designed to describe and analyze the process of taking IMCI to scale in Peru, conducted as one of five studies within the multicountry evaluation of IMCI effectiveness, cost and impact (MCE) coordinated by the World Health Organization. Trained surveyors visited each of Peru’s 34 districts, interviewed district health staff and reviewed district records. Findings show that IMCI was not institutionalized in Peru; it was implemented parallel to existing programmes to address acute respiratory infections and diarrhoea, sharing budget lines and management st...