The peppermint cultivar Todd's Mitcham forms the basis of a newly established peppermint oil industry in north-eastern Victoria. In this study the effects of Puccinia menthae on growth and yield components of Todd's Mitcham peppermint grown in pots were investigated. Rust infection significantly (P<0.05) reduced oil content, stolon number, leaf area, and root, stem, and leaf weights per plant, and increased defoliation by 67%. There was a negative linear relationship between oil yield and level of defoliation. Relationships between the amount of disease, measured as incidence and severity, and levels of defoliation were linear and logarithmic, respectively. The impact of disease on various components of growth and yield is discussed.