Background: Countries with high rates of child mortality tend to have shortages of qualified health workers. Little rigorous evidence has been done to assess how much the quality of care varies between types of health workers. We compared the performance of different categories of health workers who are trained in Integrated Management of Childhood Illness (IMCI). Methods: We analysed data obtained from first-level health facility surveys in Bangladesh (2003), Brazil (2000), Uganda (2002), and Tanzania (2000). We compared the clinical performance of health workers with longer duration of preservice training (those with >4 years of post-secondary education in Brazil or >3 years in the other three countries) and shorter duration (all other health workers providing clinical care). We calculated quality of care with indicators of assessment, classification, and management of sick children according to IMCI guidelines. Every child was examined twice, by the IMCI-trained health worker being assessed and by a gold-standard supervisor. Findings: 272 children were included in Bangladesh, 147 in Brazil, 231 in Tanzania, and 612 in Uganda. The proportions of children correctly managed by health workers with longer duration of preservice training in Brazil were 57·8% (n=43) versus 83·7% (n=61) for those with shorter duration of training (p=0·008), and 23·1% (n=47) versus 32·6% (n=134) (p=0·03) in Uganda. In Tanzania, those with longer duration of training did better than did those with shorter duration in integrated assessment of sick children (mean index of integrated assessment 0·94 [SD 0·15] vs 0·88 [0·13]; p=0·004). In Bangladesh, both categories of health worker did much the same in all clinical tasks. We recorded no significant difference in clinical performance in all the other clinical tasks in the four countries. Interpretation: IMCI training is associated with much the same quality of child care across different health worker categories, irrespective of the duration and level of preservice training. Strategies for scaling up IMCI and other child-survival interventions might rely on health workers with shorter duration of preservice training being deployed in underserved areas. Funding: Bill & Melinda Gates Foundation and the US Agency for International Development. © 2008 Elsevier Ltd. All rights reserved.