Tobacco use is a major cause of disease burden and the single most preventable cause of death in the world [1, 2]. Although smoking prevalence rates among adolescents of most European countries have declined within the last few years, smoking continues to be a serious problem, particularly in adolescents and young adults with lower educational level [3, 4].
There is limited evidence of smoking cessation interventions demonstrating efficacy in adolescents and young adults [5, 6]. In a Cochrane review of smoking cessation interventions for smokers who are younger than 20 years, approaches based on the Transtheoretical Model  achieved moderate long-term success, whereas the efficacy of psychosocial and pharmacological interventions has not been demonstrated so far . A recent review  suggested delivering (1) smoking cessation programs for youth in contexts which are geared to youth such as schools or sports clubs, (2) interventions addressing cognitive-behavioural, motivational and social influence contents, and (3) programs with at least five sessions.
Electronic communication technology such as mobile phone text messaging (SMS) has the potential to deliver smoking cessation support to large population groups. In 2010, 98% of 12-19-year-old adolescents from Switzerland owned a mobile phone; use of the mobile phone was the most frequent leisure time activity in this population group. Furthermore, reading and sending of text messages were the most frequent activities when using the mobile phone .
By use of expert system technology that provides information based on individual demographic or smoking-related characteristics, electronic communication technology can be a viable, time- and cost-saving alternative to interpersonal counselling [9, 10]. Particularly, SMS provides opportunities for individualised and interactive information delivery that may be accessed easily, independent of time and place.
To date, two randomised controlled studies were conducted to test the efficacy of SMS based smoking cessation interventions in adults motivated to quit smoking [11, 12]. Within those studies, conducted in Great Britain and New Zealand, smokers who intended to quit within the subsequent month received motivational messages and behavioural-change support over a period of 26 weeks. The messages were matched to participants' demographic and smoking-related characteristics gathered at baseline. Additionally, participants could request instant messages aimed at craving or lapse situations. Five text messages per day were sent to the participants one week before and over four weeks after a predefined quit date that was negotiated with each participant. After this period, the intervention became less intensive, with the number of messages sent being reduced from five a day to three a week until the end of the 26th week. While intention-to-treat analyses could not reveal a significant intervention effect at the 6-months follow-up in the study by Rodgers et al. , Free et al.  found significantly higher abstinence rates in the intervention than in the control group (9% vs. 4%).
Within two pilot studies in which young adult smokers, irrespective of their motivation to quit, were proactively invited to an SMS based smoking cessation intervention, high participation and retention rates could be achieved [14, 15]. To date, no randomised controlled trials testing the efficacy of smoking cessation interventions employing SMS in adolescents and young adults, or trials testing the efficacy of SMS interventions in smokers irrespective of their motivation to quit, have been reported.
Our aim is to outline the study protocol of a trial testing the efficacy of an SMS based intervention for smoking cessation in apprentices, irrespective of their motivation to quit. Apprentices have been chosen as the target population since evidence revealed high smoking prevalence rates in this subgroup of adolescents and young adults with heterogeneous educational level [4, 16].