Background: The prevalence of sexually transmitted infections (STIs) among young adults aged 18 to 25 in the U.S. is particularly high. Parental communication about sex is crucial in reducing sexual risk behaviors among this group. Due to cultural taboos about sex among Asian and Latino families, little is known about parental sex communication’s prevalence among these groups and its impact on young adults’ sexual behaviors and attitudes. Methods: This study aimed to explore the association between parental sex communication, attitudes toward sex communication, and sexual behaviors among Asian, Latino, and White young adults. A sample of 205 young adults, including 63 Asian, 48 Latino, and 94 non-Hispanic White young adults (Age M = 20.04, SD = 1.22; 68% females; 70% sexually active), completed an online survey. Results: Asian young adults reported significantly lower rates of parental sex communication (39.7%) compared to Latino (69.6%) and White young adults (67.7%) (χ2 = 14.07, df = 2, p < 0.001). Parental sex communication predicted viewing sexual topics as cultural taboos among Latino young adults (p < 0.05), subsequently predicting sexual risk behaviors like having multiple partners (β = −4.05, SE = 1.45, p = 0.03). Conclusions: Asian participants’ attitudes and sexual risk behaviors may be influenced by factors beyond familial discussions due to the lack of parental sex communication. Conversely, parental discussions among Latino participants negatively impact attitudes and behaviors related to sexual risk. Strategies for reducing sexual risk behaviors should guide parents in navigating sensitive discussions, especially within Asian and Latino families where such topics are taboo.