With new information from a recent mtDNA study, it appears that the Himalayan cuckoo is most closely related to Cuculus canorus, creating a sister-clade with the two other species: C.gularis and C.rochii. The species C.optatus, previously named horsfieldi for Palearctic populations but was proven unsuitable,  is considered a separate species because their songs were determined distinct enough.
The Himalayan cuckoo's relationship with the common cuckoo (Cuculus canorus) and its sister-clade status with C.gularis and C.rochii are highlighted by recent mtDNA studies. The species C.optatus, previously named horsfieldi for Palearctic populations but later deemed unsuitable, is now recognized as a separate species due to distinct song characteristics.