Giardiasis, an intestinal protozoan infection caused by Giardia intestinalis, is common in southeastern Anatolia,Turkey. In this cross-sectional survey, to investigate the role of giardiasis on growth and psychomotor development, we studied 160 children aged 0–5 years. Data were collected using a structured questionnaire, anthropometry, Ankara Developmental Screening Inventory, and laboratory analysis of fecal samples. The results showed that 50 per cent of the subjects were infected with at least one pathogen of intestinal parasitic infections. Giardia intestinalis was the most frequent pathogenic parasite. Giardia-infected children had a risk for stunted (OR = 7.67, 95 per cent CI = 2.25−26.16; p = 0.001) and poor psychomotor development (OR = 2.68, 95 per cent CI = 1.09−6.58; p = 0.030). The data indicate that Giardia intestinalis infection has an adverse impact on child linear growth and psychomotor development. In the primary healthcare centers, during the programme of the monitoring growth and developmental status of children, following children in terms of Giardia, diagnosis and treatment will have a positive effect on child health.