Familial chylomicronemia is an autosomal recessive disease characterised by fasting triglyceridemia and an absence of lipoprotein lipase (LpL) activity in post-heparin plasma. The disease is a result of mutation in either the lipoprotein lipase (Lpl) gene or in the apoCII gene which codes for an essential co-factor. To date, over 80 mutations in the LpL gene have been reported. The proband, a 30 month old female, presented with fasting triglycerides of 3192 mg/dl, and no detectable LpL mass or activity in post-heparin plasma. Sequencing of all of the exons and exon/intron boundaries of the LpL gene showed that she was a compound heterozygote with G-A transitions in codon 188 (G188E:GGG to GAG) generating an avall restriction site and in codon 259 (S259G:AGT to GGT) generating a bssKI site. Restriction digests confirmed the mutations and determined the incidence within the family. The father (55%LPL activity), paternal aunt (82%) and paternal grandmother (29%) were all heterozygous for the S259G mutation whilst her sister (55%), mother (73%) and maternal grandfather (45%) were heterozygous for the G188E mutation. The maternal grandmother (114%) was unaffected.