This study assessed marijuana-related content posted by adolescents on Twitter and examined content variation before and after the 2012 U.S. election legalizing recreational use in two states. For two 3-week periods occurring 6 months before and after the election, a 1% random sample was obtained of all tweets matching a set of marijuana-related queries. Original content was separated from reposted content (retweets), and foreign language tweets and those not related to marijuana were excluded. Using a structured codebook, tweet content was categorized (e.g., mention of personal marijuana use, parents' views, perceived effects.) Self-reported age was extracted from tweet metadata when available. Chi-square tests were used to assess differences in content by whether the user self-identified as an adolescent and to compare content pre- versus post-election. The full sample consisted of 71,901 tweets. After excluding nonrelevant tweets and separating original tweets from retweets, the analytic sample included 36,969 original tweets. A majority (65.6%) of original tweets by adolescents (n=1,928) reflected a positive attitude toward marijuana, and 42.9% indicated personal use. Of adolescents' tweets that mentioned parents, 36.0% of tweets indicated parental support for the adolescent's marijuana use. Tweets about personal marijuana use increased from 2012 to 2013, as did positive perceptions about the drug. Adolescents and others on Twitter are exposed to positive discussion normalizing use. Over the study period, Twitter was increasingly used to disclose marijuana use.