Introduction: Young adults (aged 17-25 years) are one group of drivers who commonly self-report using a handheld smartphone while driving. While previous research has focused on using a handheld smartphone to make or receive calls, or send and respond to text messages, smartphones have since evolved to support other features, such as video messaging. Purpose: This study extends upon previous research by applying an extended Theory of Planned Behavior (TPB), with additional predictors of moral norms, descriptive norms, and anticipated regret, to examine young drivers' intentions to use a handheld smartphone to watch video messages and read text messages while driving. Method: Young drivers (N=229, Mage=19.41, 78% female) who resided in Australia completed a 20-minute online questionnaire. Results: Reading text messages on a handheld smartphone while driving was more prevalent, with 29.7% of participants reporting sometimes to always reading a text message, and 4.4% reporting sometimes to very often watching a video message while driving. Two hierarchical multiple regressions assessed the extent to which the standard TPB constructs of attitudes, subjective norms, and perceived behavioral control (PBC; Step 1), and moral norms, descriptive norms, and anticipated regret (Step 2) predicted intentions to use a handheld smartphone to (i) watch video messages and (ii) read text messages while driving. The constructs significantly accounted for 50.8% and 45.2% of the variance in intentions to use a smartphone to watch video messages and read text messages while driving, respectively. Attitudes, subjective norms, PBC-capability, and moral norms were significant predictors of intentions to perform both behaviors. Anticipated regret was a significant predictor of intentions to watch a video message, and descriptive norms was a significant predictor of intentions to read a text message. Conclusions: Attitudes, subjective norms, PBC-capability and moral norms could be targeted by interventions to reduce handheld smartphone use while driving.