Highly pathogenic avian influenza viruses (HPAIVs) have become widespread among wildlife including within the Arctic. We summarize histopathological findings for three cases of HPAIV infection among polar bears (Ursus maritimus) inhabiting Alaska, genomically characterize viruses causing disease, and assess probable non-lethal exposures. Polar bears found dead and infected with HPAIVs exhibited meningoencephalomyelitis and neuronal necrosis, consistent with neurologic disease. Genomic sequence information obtained for H5N1 and H5N5 subtype HPAIVs associated with two cases supported epidemiologically independent spillovers. Serologic testing provided evidence for antibodies reactive to H5 and N1 antigens among most polar bears inhabiting Alaska during 2023–2024, consistent with contemporary non-lethal exposures, whereas antibodies were not found among bears sampled during 2013. These data indicate that HPAIV infection may represent an emerging threat to polar bear health within the Alaska Arctic; though, population immunity seems to be building and may protect this species from widespread demographic impacts of disease