Speech and/or language difficulties (SaLD) are among the most frequently observed developmental problems affecting children. Research points to the impact of childhood SaLD on literacy/educational achievement, behaviour and self-esteem; however, there has been limited attention paid to the impact of SaLD, directly or indirectly, on health-related qualityof-life (HRQoL). HRQoL is the impact a particular health condition (or intervention) has on an individual. HRQoL comprises numerous distinct dimensions ('domains', commonly physical, psychological and social). Very few studies have examined associations between HRQoL, SaLD, and other child and family factors and none have been undertaken in Australia. This research will explore these associations using data from a sample of children aged 4 to 9 years, extracted from the Longitudinal Study of Australian Children (LSAC), a nationally representative longitudinal study of childhood development. The rich data available in the LSAC afforded an opportunity to investigate various child and family factors that may be related to children's HRQoL and hence was well suited to exploratory research.Use of LSAC data also enabled tracking of children's outcomes over six years. The Disability-Stress-Coping (DSC) model (which examines physical health, mental health and social functioning in children with chronic illness) formed the basis for variable selection.This thesis comprises two studies, the first cross-sectional, and the second longitudinal. The cross-sectional study provided an exploration of the LSAC data and elicited variables which were appropriate for further analysis in the subsequent longitudinal investigation. Further, this study component enabled examination of relationships between HRQoL and SaLD while accounting for fine and gross motor skills which could not be examined in the longitudinal study component as there were no appropriate motor skills measures at Waves 4 and 5. The cross-sectional study involved analysis of data from the baby cohort (children aged 4-5 years) of the LSAC (n=4, 386). For this study, three domains of HRQoL were examined, assessed by the physical, emotional and social functioning subscales of the Pediatric Quality of Life Inventory (PedsQL TM ). SaLD was assessed in two ways: (1) parent concern about speech/language (Parents' Evaluation of Developmental Status) and (2) receptive vocabulary ability (adapted Peabody Picture Vocabulary Test-III).Multiple regression analyses were used to examine relationships at the cross-sectional level between HRQoL, SaLD, and various other explanatory variables including child specific factors (e.g., gender, ethnicity, temperament) and family characteristics (social-ecological considerations and psychosocial stressors).ii The longitudinal study examined the trajectory of HRQoL for children aged from 4 to 9 years and its relationship with SaLD. Generalised linear latent and mixed modelling (GLLAMM) was used to analyse data from Waves 3, 4 and 5 of the LSAC to understand HRQoL trajectories, asses...