A 16-year-old Mexican male of Japanese ancestry was found to have a new glucose-6-phosphate dehydrogenase (G-6-PD) deficient variant, named Gd(-) Tepic after the birthplace of the maternal grandmother. A younger brother was also affected and the two sisters were heterozygous. The mother, an obligatory heterozygote, did not show the abnormal variant and the possible explanation of this phenomenon is discussed. From the clinical standpoint, the propositus has had three mild hemolytic episodes while his siblings are so far asymptomatic.