Information on prevalence and type of problems of psychomotor development (PPD) is necessary for implementation of specific care programmes at field level. With the purpose of obtaining this information, a screening test, the Prueba Nacional de Pesquisa (PRUNAPE) for PPD was implemented in three health centres in San Isidro, a city near Buenos Aires, attended by different socio-economic groups: centres A and B were located in the inner city, and C in a middle-class area. The test was administered by three previously trained paediatricians to 839 apparently healthy children aged 0-5 years. The failure rates were 24%, 19% and 16% in centres A, B and C respectively (20% in total). Out of the 170 children failing the test and referred to hospital for diagnosis and treatment, only 96 complied and went through a series of studies carried out by a previously prepared multidisciplinary team. With the exception of children who failed the Battelle test [classified as Global Developmental Delay (GDD)], final diagnoses were classified according to Diagnostic and Statistical Manual of Mental Disorders, 4th edition: GDD (60 children), pervasive developmental disorders (11), communication disorders (10), motor disorders (6, of whom 2 were with cerebral palsy), attention deficit disorders (5), attachment disorders (2), normal children (3). Co-morbidity was present in 22 affected children. Forty-three per cent of children failing the test did not attend hospital or did not complete studies because of major social and family problems, the family not living in the area, or the parents preferring to consult their own paediatrician. Health centres and children not selected in a randomised way, and a significant proportion of them not complying with the indication of hospital referral were major sources of bias, so that PPD prevalences, positive and negative predictive values should be interpreted with great caution. Further studies accounting for these sources of bias are needed to confirm the observed prevalence of PPD. Training of health personnel, at hospital and health centre level, priority settings, and operational research to evaluate effectiveness of treatments and care delivery systems at field level are necessary in Argentina for optimal use of limited healthcare resources.