Although the incidence of cancer increases with age, older patients are under-represented in cancer treatment trials, resulting in limited data availability in this patient population. Here we present results from pre-defined subgroup analyses conducted by age group (<65 vs ≥ 65 years) from a randomized, double-blind, placebo-controlled phase III trial in patients with HER2-positive metastatic breast cancer. Patients who had not received previous chemotherapy or biological therapy for HER2-positive locally recurrent, unresectable or metastatic breast cancer were randomly assigned to treatment with placebo, trastuzumab, and docetaxel or with pertuzumab, trastuzumab, and docetaxel. Primary endpoint was independently assessed progression-free survival. We performed pre-specified subgroup analyses of progression-free survival according to age. The study is registered with ClinicalTrials.gov, NCT00567190. 808 patients were enrolled. Of those, 127 patients were 65 years of age or older (placebo arm: 67, pertuzumab arm: 60). Patients in both age groups experienced progression-free survival benefit with treatment in the pertuzumab arm (<65 years: HR: 0.65; 95 % CI 0.53-0.80; ≥65 years: HR: 0.52; 95 % CI 0.31-0.86). Diarrhoea, fatigue, asthenia, decreased appetite, vomiting, and dysgeusia were reported more frequently in patients 65 years of age or older compared with younger patients. Neutropenia and febrile neutropenia were reported less frequently in the older age group. The efficacy and safety data reported in CLEOPATRA suggest that the combined use of pertuzumab, trastuzumab, and docetaxel should not be limited by patient age.