A large sample of Dunedin (New Zealand) children was assessed at three, five and seven years to study the prevalence and stability of language delay, and to investigate the association between language delay at each age and low intelligence and reading problems at age seven. The prevalence of specific comprehension delay, specific expressive delay, and general language delay varied from 2.0 to 4.3 per cent. General language delays were the most stable. Every type of language delay at each age, particularly earlier, general and stable delay was associated with a significantly higher prevalence of low intelligence or reading difficulties at age seven than among the total sample.