Rationale: With several different forms of nicotine replacement therapy available for smokers, it is useful to know about factors that may influence choice of form. Objective: To examine factors associated with preference for different nicotine replacement products and effectiveness of these products. The simple comparison of success rates between the products has been reported previously. Methods: Five hundred and four smokers were invited to rank order four products (gum, patch, nasal spray and inhaler) in terms of preference and were then randomly allocated to receive one of the products for a smoking cessation attempt. They were followed up 1 week, 4 weeks, 12 weeks and 15 weeks later. Ratings of the products were repeated 1 week after the quit date. Mood and physical symptoms were assessed at baseline and at each follow-up visit. Urges to smoke were assessed at all post-quit date sessions. Abstinence was assessed by self-report with expired air carbon monoxide verification. Results: The patch was the most popular product initially, followed by the spray and inhaler and then the gum. The difference was greater for women than men. However, all smokers quickly came to like whichever product they had been allocated. Smokers who initially preferred the spray or inhaler were heavier smokers than those who preferred the gum or patch. Prior experience of the gum was associated with lower initial preference for it, but did not affect outcome. Prior experience with the patch had no effect on preference or outcome. Being allocated to the preferred product did not increase success at stopping smoking. Women were more successful at stopping smoking on the inhaler than the gum. Among highly dependent smokers, those on the inhaler had a lower relapse rate than those on the other products. Conclusions: Regardless of initial preferences, whether patients obtain their preferred form of NRT or one selected for them did not seem to affect outcome. This may be because smokers came to like particular products as they got used to them. Other things being equal, women may be better advised to use inhaler rather than gum and men vice versa.