BACKGROUND AND OBJECTIVE: To determine if cigarette smoke exposure, marijuana smoke exposure, or cytokine levels at admission to the hospital for bronchiolitis are associated with follow-up visits for asthma. METHODS: We enrolled a cohort of children aged 31 days to 2 years who were hospitalized with bronchiolitis from January 2013 to April 2014. Data included the results of a baseline survey about children's health and demographics, nasal wash samples, the results of a 6-month postdischarge follow-up survey, and a chart review. Nasal wash samples were tested for interleukin (IL)-6, IL-13, and tumor necrosis factor a (TNF-a); values were categorized for analysis. x2, Fisher's exact, and Wilcoxon rank tests were done to test bivariable differences; all analyses were done using SAS. RESULTS: We approached 180 families for enrollment; 99 consented to participate, and 74% of these completed follow-up surveys. Half of those with high levels of IL-13 had follow-up visits for asthma, whereas only 4.2% of those with low levels had follow-up visits for asthma (P 5 .02). Marijuana exposure was reported for 12.5% (n 5 7) of study participants. There was a significant association between marijuana exposure and TNF-a levels (P 5 .03). CONCLUSIONS: Our study revealed an association between IL-13 and follow-up visits for asthma in children who were hospitalized with bronchiolitis. We found an association between family-reported marijuana smoke exposure and detectable but lower levels of TNF-a. Further research is needed to study these relationships.