Previous research indicates loneliness affects physiological and quality of life outcomes in oncology populations. However, minimal research has been conducted specifically on bone and blood marrow transplant (BMT) patients (Knight et al., 2013). To further explore this issue, we conducted a preliminary study to examine the relationship of loneliness with quality of life, immunological functioning, and other health indicators at six months post-transplant in BMT patients. The Functional Assessment of Cancer Therapies–BMT (FACT-BMT) was used to measure QOL and the UCLA Loneliness Scale Version 3 was used to assess general loneliness and loneliness experienced during hospitalization. We found that experiencing loneliness during hospital stay and experiencing loneliness in general was negatively associated with overall quality of life six months after a BMT. Specially, hospital loneliness was associated with poorer social well-being and poorer functional well-being; and loneliness in general was associated with poorer social well-being. In addition, loneliness during hospitalization was related to difficulty managing disease symptoms six-months after a transplant. Hospital loneliness was associated with higher neutrophil counts to monocyte counts 30 days after BMT, which is an indicator of poorer overall survival rate. However, loneliness during hospital stay was not associated with neutrophil to lymphocyte ratio. These results indicate that there is a relation between loneliness experienced during hospitalization and immunological functioning which may adversely impact recovery from a bone marrow transplant.