Aim: To evaluate the long-term effects of a zinc acetate and chlorhexidine diacetate mouth rinse (Zn/CHX) on intra-oral halitosis. Materials and methods: Forty-six adults with intra-oral halitosis were randomized into a 6-month, double-blind, placebo-controlled clinical study. The presence of intra-oral halitosis was evaluated at baseline, 3 and 6 months after treatment by assessment of organoleptic score (OLS) and by total volatile sulphur compounds (T-VSC), hydrogen sulphide (H2S) and methyl mercaptan (MM) concentrations in exhaled air. Results: A Zn/CHX mouth rinse provided significantly better control of intra-oral halitosis than a placebo mouth rinse. At 3 and 6 months, individuals rinsing with the Zn/CHX rinse presented with reductions of the OLS, T-VSC (p <.01, respectively), H2S (p <.001), and MM (p <.01) in subjects’ exhaled air. At 6 months, 68.2% of individuals using the Zn/CHX rinse experienced a 1 or 2 category improvement in OLS compared with 19.1% of placebo-treated subjects. 91% of subjects in the Zn/CHX group were categorized as being effectively treated for intra-oral halitosis (i.e. H2S < 112 ppb), compared to 43% in the placebo group. Conclusion: Zn/CHX mouth rinse provides effective long-term efficacy against intra-oral halitosis, assessed both objectively and subjectively. With regular rinsing, the effect was sustained for 6 months. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd