The prevalence of carbapenem-resistant Acinetobacter baumannii in Saudi Arabia and their resistance genetic mechanisms are yet to be identified. We studied the prevalence and genetic diversity of extended-spectrum beta-lactamase genes, particularly the PER-1 gene, among carbapenem-resistant A. baumannii strains from patients at a tertiary care hospital in Riyadh, Saudi Arabia between 2006 and 2014. Fresh subcultured samples were tested for antimicrobial susceptibility minimum inhibitory concentration (MIC). Total genomic DNA was extracted from each isolate and further used for polymerase chain reaction (PCR) genotyping, sequence-based typing (SBT) of PER-1 and OXA-51-like gene, and multilocus sequence typing (MLST) of positive isolates. Randomly selected clinical isolates (n = 100) were subjected to MLST. A total of 503 isolates were characterized as multidrug-resistant (MDR) using the MIC. Isolates were further PCR tested for bla and bla resistance genes (n = 503). The genotyping results showed that 68/503 (14 %) isolates were positive to bla TEM. The genotyping results of PER-1-like genes showed that 384/503 (76.3 %) were positive among MDR Acinetobacter isolates. Based on SBT, the majority of these isolates were clustered into three main groups including isolates harboring PER-1: AB11 (bla ), isolate AB16 (bla), and, finally, the plasmid pAB154 (bla ). Remarkably, many isolates were concealing the PER-1 gene and harboring the TEM resistance genes as well. MLST results for selected isolates (n = 100) identified four main sequence types (STs: 2, 19, 20, and 25) and four novel isolates (ST 486-489). We report 76.3 % prevalence of the PER-1 resistance gene among Acinetobacter clinical isolates from Riyadh, Saudi Arabia. Further work is needed to explore the clinical risks and patient outcome with such resistance related to healthcare-associated infections and investigate the genetic and molecular mechanisms that confer the MDR phenotype.