This study aimed to conduct quantitative and qualitative analyses of anonymous data from an immunisation hotline call centre over equal periods in 1999 and 2003. Transcripts for all telephone calls in two periods were analysed using thematic and descriptive statistical analyses and significance testing of comparisons made between data from the two periods. Caller numbers increased from 1010 in 1999 to 3413 in 2003. There was a significant increase in service utilisation by both the public (mostly parents) and health professionals, especially by general practice nurses. The nature of the enquiries shifted according to schedule changes and media stories. Findings are discussed in the context of prominent issues at that time, and suggestions are made for improving communication to meet the needs of both the public and health professionals.