Objective To investigate the contribution of poor case management and care-seeking behaviour to childhood deaths from acute respiratory infections (ARI) and diarrhoeal diseases in rural Mexico. Methods Eighty-nine deaths from ARI and diarrhoea in under-fives from Hidalgo over a 7-month period were identified from registered death certificates. We interviewed the carers of 75 of these children, eliciting what happened before death, including signs and symptoms, contact with health services, details on treatments and details of doctors. These death narratives were used to assess the contributions of care seeking and case management to the childhood deaths. We conducted an independent investigation of the clinical competence of doctors mentioned in the death narratives using standard case scenarios and compared this with results obtained from neighbourhood control doctors. Results Late care seeking and/or poor case management contributed to 68% of deaths. The estimated contribution of care seeking alone was 32%, of case management alone 17% and of both care seeking and case management 18% of deaths. Doctors implicated as having contributed to a child's death had significantly lower clinical competence scores than those who were not. Private doctors accounted for 1.4 times more consultations prior to death than public doctors, but were implicated in 1.8 times the number of deaths. Conclusion Efforts to reduce child mortality need to improve both care seeking for childhood illnesses and quality of case management. It is essential that doctors in the private sector be included, as in Mexico and many other countries they provide a large proportion of care, often with adverse outcomes.