Poor sleep is very common in patients in the ICU and hence, sleep quality is considered an important aspect of intensive care; however, the underlying mechanisms of poor sleep in patients in the ICU remain unknown. In this study, we aimed to explore the role of rs3750625, which is located in the 3'UTR of adrenoceptor alpha 2A (ADRA2A), in sleep quality. For this purpose, luciferase assay was conducted to investigate the association between miR‑34a and ADRA2A, and the effect of rs3750625 on the binding affinity between miR‑34a and ADRA2A was examined. RT‑qPCR and western blot analysis were carried out to examine the regulatory association between miR‑34a and ADRA2A. The differences in sleep time and efficiency were compared between groups carrying the AC and CC genotypes of rs3750625, respectively. According to the results from an online search, miR‑34a could directly bind to the 3'UTR of ADRA2A, and such binding was confirmed by the observation that miR‑34a inhibited the luciferase activity of major or minor ADRA2A 3'UTR in a dose‑dependent manner in HCN‑1A and U251 cells. In addition, the ADRA2A protein and mRNA levels in the HCN‑1A and U251 cells were evidently decreased following transfection with miR‑34a precursors. Notably, patients in the AC group exhibited a similar level of miR‑34a mRNA expression compared with patients in the CC group; however, the ADRA2A mRNA and protein levels in the CC group were significantly increased in comparison with those in the AC group. In addition, the sleep time and sleep efficiency in the CC group were much higher than those in the AC group. Furthermore, the mean arterial pressure (MAP) values in both the AC and CC groups remained stable from 22:00 to 08:00, and the respiratory rates in both groups were quite similar. However, the heart rate of patients in the CC group was much lower than that of patients in the AC group. On the whole, the findings of this study suggest that the genetic variant rs3750625 in the 3'UTR of ADRA2A affects the sleep quality of patients in the ICU by promoting the binding of miR‑34a to ADRA2A, and hence it may serve as a novel biomarker for the prediction of the sleep quality of patients in the ICU.