The funtioning of families of children with developmental disabilities has been of interest to researchers for some time. To date, little research has focused on experiences of New Zealand families. The aim of this research is to investigate relationships between various aspects of the family environment and family functioning, and to explore siblings' level of self-concept and satisfaction with the sibling relationship. It is expected that families who receive more support from external levels of the environment will be able to function more effectively in their immediate environment (Bronfenbrenner, 1979; Hornby, 1994). Twenty-one parents and nineteen siblings of children with developmental disabilities volunteered to take part in this study. Parent participants completed questionnaires about family demographics, the level of support received from external sources, their perceptions of the family environment, and level of stress related to child characteristics; pessimism and family problems. Sibling participants completed questionnaires about their satisfaction with the relationship with their brother or sister, their self-concept, and their own perceptionso of the family environment. The results indicate that there are a number of relationships between various aspects of the environment and family functioning. Siblings who are more satisfied with their relationship have higher self-concept scores, however the self-concept scores were lower than expected. Families who receive higher levels of support have more positive perceptions of the family enviornment, and families who have more support and more positive views of the environment have few concerns on the resources and stress scale. The results indicated that families consider that they are receiving adequate support from professional services, however support from family and friends appears to be lacking. This study has provided insight into the functioning of New Zealand families who have children with developmental disabilities, and has suggested a number of avenues for future research.