Newborn cystic fibrosis (CF) screening facilitates early diagnosis and nutritional intervention, which prevents malnourishment and improves growth in childhood. To provide baseline information on the natural history of CF in the Republic of Ireland, where newborn screening has not yet been introduced and CF incidence is high (1:1353 live births), we examined the effect of presentation mode, symptom type and gender on age at diagnosis. Median age at diagnosis was calculated by gender and for presentation mode/symptom type for 601 CF registry children diagnosed 1986-2007. Modes of presentation were each significantly associated with delayed presentation. An adjusted odds ratio of 4.5 (95% CI: 1.8, 11.1) was determined for presentation with family history, 43.1 for gastrointestinal symptoms presentation (95% CI: 18.3, 101.4), 96.9 for both respiratory and gastrointestinal symptoms (95% CI: 38.6, 243,4), and 115.4 for respiratory symptoms (95% CI: 45.2, 294.7). Children with respiratory symptoms had the greatest likelihood of delayed diagnosis (median age: 20.4 months), followed by those with respiratory and gastrointestinal symptoms (9.2 months). Gender was not significantly associated with a delayed presentation when presentation mode was taken into account.