The "murtilla" (Ugni molinae Turcz., Myrtaceae), present in Contulmo Natural Monument (Araucanía Region, Chile), is affected by witches' broom disease, caused by the presence of a phytoplasma in the sieve tubes of the phloem. This phytoplasma affects plants morphoanatomically, producing evident symptoms. Infected branches show reddening of leaves and general dwarfism. In the present study, we compared morphoanatomically and physiologically branches (modules) of murtilla with and without symptoms of witches' broom disease. This was done in order to quantitatively evaluate the actual effect of the infection on adult plants. We cut branches of similar age, with and without symptoms, where we measured fluorescence, chlorophyll content, specific leaf area, stem size, pith size, and vessel size and number. We also measured fruit traits in symptomatic and asymptomatic plants. We did not found differences in the Fv/Fm (maximun efficiency of the PSII) and total chlorophyll content between symptomatic and asymptomatic modules. However, symptomatic modules had lower pith area, vessel size, and leaf area, and dry weight than asymptomatic modules. Infected plants also had less fruits per plant and with less total soluble solutes (TSS) in the fruits compared to healthy plants, although average individual fruit weight was similar between symptomatic and asymptomatic plants. Witches' broom disease affects the anatomy, morphology, and quality and quantity of fruits of murtilla plants. However, the disease does not seem to affect some physiological parameters. The murtilla in Chile has high economical potential as an edible fruit and in the cosmetic and pharmaceutical industry. Future studies should focus on the vector of the disease and the possible effects of the infection on other commercially-relevant traits.