Immigrants with cancer often have professional and/or family interpreters to overcome challenges communicating with their health team. This study explored the rate and consequences of nonequivalent interpretation in medical oncology consultations. Consecutive immigrant patients with newly diagnosed with incurable cancer, who spoke Arabic, Cantonese, Mandarin, or Greek, were recruited from the practices of 10 medical oncologists in nine hospitals. Their first two consultations were audio taped, transcribed, translated into English and coded. Thirty-two of 78 participants had an interpreter at 49 consultations; 43% of interpreters were family, 35% professional, 18% both a professional and family, and 4% a health professional. Sixty-five percent of professional interpretations were equivalent to the original speech versus 50% for family interpreters (P= .02). Seventy percent of nonequivalent interpretations were inconsequential or positive; however, 10% could result in misunderstanding, in 5% the tone was more authoritarian than originally intended, and in 3% more certainty was conveyed. There were no significant differences in interpreter type for equivalency of interpretations. Nonequivalent interpretation is common, and not always innocuous. Our study suggests that there may remain a role for family or telephone versus face-to-face professional interpreters. careful communication between oncologists and interpreters is required to ensure optimal communication with the patient.