BACKGROUND: A big proportion of populations in sub-Saharan Africa still battle with poverty and intense exposure to infections including chronic worm infections. Studies of cognitive effects of worms have not been consistent regarding which functions are affected and whether deworming is beneficial. However, executive functions could be particularly susceptible to impairment. The home environment is reported to affect child development. However, its unique contribution in Ugandan children exposed to various factors has not been estimated. This PhD research therefore aimed to [I] examine effects of maternal and childhood worm infections and their treatment on executive function and other developmental outcomes in infancy and preschool-age children; and [2] investigate the independent effects of the home environment on child mental performance, taking into account the confounding effects of other socio-demographic exposures. In the same sample, [3] relationships between executive functions were examined in order to understand how they may be disrupted by worms and other adverse factors. METHODS: This research was conducted within the ongoing Entebbe Mother and Baby Study (EMABS) in which 2500 pregnant women were randomised to receiving a single dose of albendazole or placebo and praziquantel or placebo in a 2x2 design. 983 infants born to these women were assessed at age 15 months on executive function, and other abilities to measure the effect of maternal worm infections and their treatment on these functions. The infants were then randomised to quarterly doses of albendazole or placebo from age 15 months and were assessed again at age five years (N=870) on measures of executive function, general ability and motor function to examine effects of childhood worm infections and their treatment on performance on these functions. Relevant health and socio-demographic date were collected and used in the analyses. 200 children were assessed on an extended battery of executive function measures and their scores were used to explore the structure and relationships between executive functions . Home environments of 163 children were examined using an adapted version of the Home Observation for Measurement of the Environment (HOME). RESULTS: Maternal Mansonella perstans and Strongyloides stercoralis infection were negatively associated with infants' performance on the A not B task (a measure of executive function) and language respectively but anthelminthic treatment did not show significant effects overall. In childhood, worms were negatively associated with performance on measures of working memory (Verbal Fluency, Counting Span, and Running Memory), attention (Picture Search), and general ability (Block Design). However, treatment with quarterly albendazole did not have significant effects on performance on measures of cognitive functioning. The home environment contributed to cognitive performance above and beyond the effect of other factors. Low-to-moderate inter-construct correlations were observed among executive functions and three components were extracted from the four domains. Planning was most related to inhibition with working memory also contributing to the best fit model. CONCLUSION: Both infant and childhood developmental outcomes suggest that executive functions may particularly be susceptible to impairment by worm infections but treatment may not reverse the effects. Furthermore, the results show that the home environment affects the child independently of SES, parental education and other global measures. Correlations and factor loadings indicate unity among the executive functions, particularly between planning and a combination of inhibition and working memory,