INTRODUCTION: Despite a substantial increase in use of SMS text messages for collecting smoking-related data, there is limited knowledge on the parameters of response. This study assessed response rates, response speed, impact of reminders and predictors of response to text message assessments among smokers. METHODS: Data were from two SMS cessation intervention trials using clinical samples of pregnant (n = 198) and general smokers (n = 293) sent text message assessments during 3-month cessation programs. Response rates were calculated using data from the host web-server. Changes in response over time, impact of reminders and potential demographic (age, gender, ethnicity, parity, and deprivation) and smoking (nicotine dependence, determination to quit, prenatal smoking history, smoking status at follow-up) predictors of response were analyzed. RESULTS: Mean response rates were 61.9% (pregnant) and 67.8% (general) with aggregated median response times of 0.35 (pregnant) and 0.64 (general) hours. Response rate reduced over time (P = .003) for general smokers only. Text message reminders had a significant effect on response (Ps < .001), with observed mean increases of 13.8% (pregnant) and 17.7% (general). Age (odds ratio [OR] = 0.95, 95% confidence interval [CI] 0.90-1.00) and deprivation (OR = 0.98, 95% CI 0.96-1.00) weakly predicted response among pregnant smokers and nonsmoking status at 4 weeks follow-up (OR = 8.63, 95% CI 3.03-24.58) predicted response among general smokers. CONCLUSIONS: Text message assessments within trial-based cessation programs yield rapid responses from a sizable proportion of smokers, which can be increased using text reminders. While few sources of nonresponse bias were identified for general smokers, older and more deprived pregnant women were less likely to respond. IMPLICATIONS: This study demonstrates that most pregnant and general smokers enrolled in a cessation trial will respond to a small number of questions about their smoking sent by text message, mostly within 1 hour of being sent the assessment text message. For those who do not initially respond, our findings suggest that 24- and 48-hour text message reminders are likely to increase response a small but meaningful amount. However, older age and higher deprivation among pregnant smokers and relapse among general smokers is likely to reduce the chance of response.