Objectives The prevalence of malnourishment among paediatric cancer patients undergoing chemotherapy in developing countries is poorly documented despite greater potential for malnourishment in such settings. We aimed to estimate the prevalence of malnourishment among paediatric cancer patients in Mexico City, and assess the association between malnourishment and length of hospital stay.

Methods Individuals eligible for this study were paediatric cancer patients (aged <18 years) admitted to Hospital Infantil de Mexico Federico Gomez (Mexico City) with febrile neutropaenia. Our exposure of interest, malnourishment, was defined as an age-adjusted and sex-adjusted z-score<−2 (ie, 2 SDs below the expected mean of the WHO reference population). We estimated time ratios (TRs) and 95% confidence limits (CLs) for the association between malnourishment and length of hospital stay.

Results Our study population comprised 111 paediatric cancer patients with febrile neutropaenia, of whom 71% were aged <10 years and 52% were males. The prevalence of malnourishment was 14%, equal to a 530% (standardised morbidity ratio=6.3; 95% CL 3.7, 10) excess of malnourishment compared with the world reference population. The median length of hospital stay for malnourished patients was 15 days, which corresponded with a 50% (TR=1.5, 95% CL 1.0, 2.3) relative increase in length of stay compared with patients who were not malnourished. Patients with body mass indices equal to the mean of the world reference population had the shortest length of stay.

Conclusions Future studies should explore potential interventions for malnourishment to reduce the length of hospital stay or other established adverse consequences of malnourishment.