OBJECTIVES: We examined the association between multimorbidity with or without mental illness and patient-physician communication and trust among Medicare beneficiaries with at least one chronic physical condition. METHODS: Medicare Current Beneficiary Survey (2012) was used to assess patient-physician communication and trust among community-dwelling elderly Medicare beneficiaries (Age >64 yrs; N= 9,867) with following multimorbidity categories: 1) No MM: Single physical condition, 2) MM-PI: >2 physical conditions but no mental illness, and 3) MM-PI&MI: Both physical and mental conditions. RESULTS: As compared to no MM, those with MM-PI were more likely to agree that their doctor is often in hurry (AOR [95%CI]:1.73 [1.39, 2.15]), patient often has health problems that should be discussed but are not (1.37 [1.03, 1.81]), and less likely to agree that doctor tells them all they want to know about their condition and treatment (0.60 [0.42, 0.86]). Further, elderly with MM-PI were less likely to agree that doctor is very careful to check everything when examining them (0.55 [0.35, 0.85]). Patient-physician communication and trust worsened among those with both chronic physical and mental conditions. In addition to above factors, those with MM-PI&MI were more likely to agree that doctor often does not explain their medical problems to them (1.48 [1.12, 1.95]), and less likely to agree that doctor answers all questions (0.39 [0.21, 0.74]) as compared to those with no MM. With respect to trust in doctor, elderly with MM-PI&MI were less likely to agree that doctor has complete understanding of their illness (0.52 [0.33, 0.84]), and patient has great confidence in doctor (0.41 [0.25, 0.67]) as compared to those with no MM.  CONCLUSIONS: Multimorbidity is a barrier to patient-physician communication and trust. Spending more time with patients, explaining patients’ illnesses and treatments, and having a good understanding of all of patients’ medical conditions are required especially among elderly having multiple chronic physical conditions with mental illness.