Aim: To investigate to what extent smokers and snus users in Sweden consider and plan their quit attempts in advance, and to assess if spontaneity is associated with success. Methods: A sample of 5999 Swedish men and women between 16 and 80 years were interviewed via telephone about current and former smoking and snus use and their latest quit attempts. Results: Among 2272 ex-smokers and current smokers who had ever made a serious quit attempt 48% reported to not having planned their latest attempt in advance. Furthermore, 40% reported to not even having considered giving up smoking before they actually made the attempt. Of 809 former and current snus users 48% did not plan, and 44% did not consider quitting in advance. Smokers and ex-smokers were more likely to remain smoke-free for at least six months if the attempt was unplanned (sex and age adjusted OR=2.6; 95% CI=1.7-3.8). When dividing the smoking quit attempts into considered versus not considered the advantage of the spontaneous attempts remained (adjusted OR=1.9; CI=1.3-2.9). The corresponding analyses of snus use quitting showed similar advantages for the unplanned and the not considered quit attempts. Conclusions: In Sweden, a considerable proportion of the attempts to quit smoking, as well as to quit using snus, are made without prior consideration or planning. Spontaneous quit attempts appear to have a greater chance of long-term success than those preceded by consideration or planning.