A previously unknown hemoglobin (Hb) variant was detected during measurement of glycosylated Hb (Hb A_1c) after the introduction of a new high performance liquid chromatography (HPLC) apparatus. Subsequent DNA sequencing revealed a heterozygous single nucleotide substitution at codon 79 (C>A) on the β-globin gene changing an amino acid [β79(EF3)Asp→Glu; HBB: c.240C>A]. The new Hb variant was named Hb Kalundborg after the place of origin of the proband. Heterozygosity for this mutation appears to have no clinical significance in itself except for a possibly slightly lower oxygen affinity. However, it interferes with Hb A_1c measurement by HPLC, causing a falsely high Hb A_1c concentration when using the G11 apparatus with clinical implications possibly to follow.