Transgender and gender diverse people often face discrimination and may experience disproportionate emotional distress that leads to suicide attempts. Therefore, it is essential to estimate the frequency and potential determinants of suicide attempts among transgender and gender diverse individuals. Longitudinal data on 6,327 transgender and gender diverse individuals enrolled in 3 integrated healthcare systems were analyzed to assess suicide attempt rates. Incidence was compared between transmasculine and transfeminine people by age and race/ethnicity and according to mental health status at baseline. Cox proportional hazards models examined rates and predictors of suicide attempts during follow-up. Data were collected in 2016, and analyses were conducted in 2019. During follow-up, 4.8% of transmasculine and 3.0% of transfeminine patients had at least 1 suicide attempt. Suicide attempt rates were more than 7 times higher among patients aged <18 years than among those aged >45 years, more than 3 times higher among patients with previous history of suicide ideation or suicide attempts than among those with no such history, and 2-5 times higher among those with 1-2 mental health diagnoses and more than 2 mental health diagnoses at baseline than among those with none. Among transgender and gender diverse individuals, younger people, people with previous suicidal ideation or attempts, and people with multiple mental health diagnoses are at a higher risk for suicide attempts. Future research should examine the impact of gender-affirming healthcare use on the risk of suicide attempts and identify targets for suicide prevention interventions among transgender and gender diverse people in clinical settings.