Background: Sex differences in cardiac arrhythmias are well-established and partly attributed to sex hormones. Aim: We aimed to explore the prevalence of arrhythmias in transgender and nonbinary ( TGNB ) adults. Methods: This cross-sectional study utilized patient electronic medical records from a single community healthcare center specializing in TGNB care. Adults aged ≥18 years with ≥2 medical visits between January 1, 2010, and December 31, 2021, were categorized into self-reported gender groups as TGNB (transgender man[TGM], transgender woman[TGW], nonbinary-assigned male at birth, nonbinary-assigned female at birth) and cisgender (cisgender man[CisM] or cisgender woman[CisW]). We categorized arrhythmias as atrial, ventricular, or other. Descriptive statistics characterized the prevalence of arrhythmias by gender group. Age- and race-adjusted Firth-type logistic regression models compared TGNB patients to CisM and CisW. The prevalence of arrhythmias was also descriptively explored in nonbinary people and in TGNB people with a gender-affirming hormone therapy (GAHT) prescription. Results: Among 49,862 adults, 7121 (14%) identified as TGNB persons. Participants were young (median age 28 years-old) and prevalence of arrhythmias was low (0.7-1.4% in nonbinary persons, 1.4-1.5% in transgender persons). Adjusting for age and race, TGM and TGW had a similar risk of arrhythmias compared to CisM (TGW: OR=0.89 (0.63-1.24), p=0.52; TGM: OR=1.17 (0.82-1.62), p=0.37), but statistically significantly higher odds of arrhythmias compared to CisW (TGW: OR=1.65 (1.13-2.34), p=0.01; TGM: OR=2.15 (1.48-3.04), p<0.01). Prevalence of arrhythmias appeared similar among TGNB adults who used GAHT and those who did not (1.5% vs 1.9% in TGM, 1.2% vs 2.1% in TGW). Conclusion: Further research examining arrhythmias in TGNB patients and across gender minority subgroups is warranted, including longitudinal studies evaluating the potential impact of GAHT.