The purpose of this study is to (1) identify addiction symptoms that are uniquely associated with mobile phone use among adolescents in Korea; (2) examine how background characteristics are related to addiction symptoms; and (3) explore how background characteristics, motives, and the amount of mobile phone use predict addictive use of mobile phones. Using a survey of 550 adolescents in Korea, this study identified three addiction symptoms: intrusion, attachment, and withdrawal. The regression models suggest that background characteristics, including impulsivity, peer conformity, imitation, and social anxiety, strongly explain the variance of addictive symptoms. Results show that instrumental motives for using the mobile phone are positively related to addictive behaviors. The amount of mobile phone use was positively related to addiction, even though the percentage of the variance explained in the regression models was small