Objectives: Cigarettes vary in rod length but are generally thought of as a constant unit. In this study, we evaluated whether the rod length of participants' usual brand cigarettes affected their perceptions and smoking habits when switching to SPECTRUMs. Methods: Data were analyzed for 341 participants smoking their own brand cigarettes for one week and after switching to normal nicotine content (11.6 mg) SPECTRUMs for 2 weeks. Changes in perceptions of cigarette attributes and biomarkers of smoke exposure were evaluated using linear mixed models among 3 groups: usual length short (ULS, 72 mm); medium/king (ULM, ~84 mm); and long (ULL ≥ 100 mm). Results: Among the 3 cigarette length groups, only ULL smokers' rated SPECTRUMs significantly less strong, harder to draw, lower in taste, and lower in enjoyment (p < .03) compared to usual brand. Among all groups, satisfaction was significantly lower for SPECTRUMs (p < .02). Cigarettes per day (CPD) increased significantly more for ULL (+4.75 CPD) as compared to ULM (+1.38 CPD) (p < .001). When switching to SPECTRUMs, cotinine-per-cigarette decreased among all groups, and exhaled carbon monoxide increased significantly in ULL and ULM smokers (p < .001). Conclusion: People who smoked long cigarettes had the largest changes in perceptions and use when switching to SPECTRUM research cigarettes.