The percentage of the population involved in the Christian church in New Zealand has been declining since the middle of the 1960s. Most seriously affected has been the mainline Protestant denominations such as Presbyterian, Anglican and Methodist. This article analyses and presents data collected by the National Church Life Survey New Zealand 2001 on churches in New Zealand and compares these figures with New Zealand census data collected in 2001. The results indicated that this sector of the church is heavily overrepresented in the older age groups and underrepresented in the younger age groups. The average age for adults over 15 is 58 years of age for Anglicans, 62 for Presbyterians, 65 for Cooperating Parishes and 66 for Methodists compared to 54 for Catholics, 43 for Baptists and an average age of 41 years for the general population of New Zealand. This situation is a consequence of the significant loss of the baby boomer generation as young adults in the 1960s and 1970s, with its ongoing impact on the relationship to church of subsequent generations. However, surprisingly the census data revealed that the age representation is much more evenly spread when church affiliation, rather than attendance, is indicated. This suggested that young adults are still identifying themselves as Anglican, Presbyterian and Methodist even if they do not choose to belong. Implications for the future of the church and its mission are discussed. (Contains 4 tables and 1 figure.)