In chronic hepatitis B (CHB), hepatitis D virus (HDV) superinfection can lead to acute liver failure. The incidence of HDV superinfection is unknown, but is often detected in immigrants from HDV endemic countries. In this report, we characterize long-term clinical and virological outcomes in a hepatitis B virus (HBV) infected carrier before and after HDV superinfection, acquired from their spouse having HBV/HDV co-infection. A 38 year-old Mongolian male with CHB on anti-HBV therapy developed acute liver failure following HDV superinfection. Although he recovered, avoiding the need for liver transplant, HDV serological and molecular markers of infection persisted for the subsequent 16-month follow-up period, suggesting the development of CHB/HDV co-infection. The source of his HDV was from his wife of 10 years, a 34-year old Mongolian female known to have inactive CHB/HDV co-infection but who was not on anti-HBV therapy. Phylogenetic analysis of the complete HDV genome from the couple showed >99% similarity, with post-transmission longitudinal sequence revealing specific nucleotide substitutions between both spouse\'s HDV genome sequences. This study highlights the ongoing risk of HDV superinfection due to long-term co-habitation or sexual transmission in CHB patients. The fact that transmission occurred after almost a decade of marriage may be due to host immune or environmental factors that created a more favorable condition for transmission.