Primary Immune Deficiency disorders (PIDs) are uncommon conditions, which necessitate urgent diagnosis in order to prevent disabling complications such as bronchiectasis. Timely diagnosis can be life-saving in children with PIDs such as severe combined immune deficiency.A customised molecular diagnostic service was established in New Zealand in 2005. Most patients referred to the service have undergone genetic counselling before blood was drawn for testing. Genomic DNA was extracted and polymerase chain reaction (PCR) performed to amplify genes of interest, followed by DNA sequencing. The DNA sequences were then aligned with wild type sequence using computer software to identify possible mutations.Mutational analysis was undertaken in 27 probands with suspected PID. Seven causative mutations were identified in these patients. Family studies have been undertaken after genetic counselling.Customised genetic testing is a cost-effective and efficient method for PID diagnosis in a small developed country.