Background Adult cancer patients consider diminished sleep quality as one of the most distressing symptoms they face. Furthermore, the significant correlation between insomnia and increased risk of death and loss to follow-up underscores the importance of enhancing sleep quality in this population. A growing number of cancer patients are practising yoga to manage symptoms and side effects of treatment, including sleep-wake disturbances. A systematic review of the evidence is necessary to examine whether yoga practice eads to improved sleep quality among adult cancer patients undergoing cancer treatment. Objectives The primary objective of this systematic review was to identify the effectiveness of yoga practice in adult cancer patients over the age of 18 who were concurrently undergoing conventional treatment for cancer. Inclusion criteria Types of participants This review considered studies that included adults over the age of 18 years diagnosed with cancer (regardless of the type of cancer, stage or presence of co-morbidities) who were concurrently undergoing conventional treatment for cancer (regardless of treatment modality, intensity, delivery, frequency, or duration of treatment). Types of intervention(s)/phenomena of interest This review considered studies that evaluate the effects of yoga intervention (regardless of mode of delivery, timing, frequency and duration) on sleep quality among adult cancer patients over the age of 18 years who were concurrently undergoing conventional treatment for cancer. Types of studies The review considered any randomized controlled trials (RCT); other research designs, such as non-randomized controlled trials and before and after studies, were also considered for inclusion to enable the identification of current best evidence regarding yoga practice. Types of outcomes The primary outcome measure was sleep quality. Search strategy Published and unpublished studies in the English language were identified from seven electronic databases. Searches were completed in April 2013. Methodological quality Methodological quality was assessed by two independent reviewers using the standardized critical appraisal instrument from the Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument. Data collection Data were extracted using the standardized data extraction tool from the Joanna Briggs Institute. Data synthesis Statistical pooling was not possible due to heterogeneity of the studies; therefore findings were presented as a narrative. Results Five RCTs met the inclusion criteria for this systematic review. Of the five RCTs reviewed, three indicated that yoga participants had less sleep disturbance and insomnia than controls, while two studies found no group differences. Conclusions Findings from this review offer some evidence that yoga practice may improve sleep quality among adult cancer patients undergoing cancer treatment by decreasing sleep disturbance and insomnia.