This study investigates an outbreak of Middle East Respiratory Syndrome (MERS) at King Fahad Medical City (KFMC) in Riyadh, Saudi Arabia, from March 29 to May 21, 2014. The outbreak involved 45 patients, including 8 with external infections, 13 long-term inpatients, 23 healthcare workers (HCWs), and 1 with an indeterminate source. Molecular epidemiological analysis of MERS-CoV sequences from 10 patients and a partial sequence from another patient revealed that this outbreak was part of a larger outbreak affecting multiple healthcare facilities in Riyadh, possibly originating from a single zoonotic transmission event in December 2013. The findings suggest continued healthcare-associated transmission for 5 months. The study highlights the importance of complete viral genome sequencing in outbreak investigations and the need for enhanced infection control measures.This study investigates an outbreak of Middle East Respiratory Syndrome (MERS) at King Fahad Medical City (KFMC) in Riyadh, Saudi Arabia, from March 29 to May 21, 2014. The outbreak involved 45 patients, including 8 with external infections, 13 long-term inpatients, 23 healthcare workers (HCWs), and 1 with an indeterminate source. Molecular epidemiological analysis of MERS-CoV sequences from 10 patients and a partial sequence from another patient revealed that this outbreak was part of a larger outbreak affecting multiple healthcare facilities in Riyadh, possibly originating from a single zoonotic transmission event in December 2013. The findings suggest continued healthcare-associated transmission for 5 months. The study highlights the importance of complete viral genome sequencing in outbreak investigations and the need for enhanced infection control measures.