The Mini-Mental Adjustment to Cancer Scale (Mini-MAC) is a 29-item instrument designed to evaluate the responses developed by cancer patients during their mental adjustment to diagnosis and treatment.This study aims to validate the Mini-Mental Adjustment to Cancer Scale (Mini-MAC) translated and adapted to the Portuguese language and culture, in end-of-life cancer patients receiving palliative care.The instrument was administered to 346 Portuguese end-of-life cancer patients, receiving care through outpatient visits or admitted into palliative care units, without cognitive symptoms and with symptoms under control. A cross-sectional validation study using orthogonal rotation through the varimax method followed by convergent and discriminant validity.The analysis of the main components confirms the existence of five factors, demonstrating the validity of the construct, with good internal consistency in the subscales and Cronbach's alpha values between 0.78 and 0.93. Good test-retest reliability was also found, and r values for subscales ranged from 0.62 to 0.99.The instrument proved to be a reliable, valid and sensitive measure in the study of mental adjustment of Portuguese end-of-life patients with cancer receiving palliative care.Nurses can use the Mini-MAC Scale in research and clinical practice in order to evaluate the mental adjustment of Portuguese end-of-life cancer patients receiving palliative care.