Objective To evaluate the neuropsychology and cognitive ability changes in patients with primary insomnia (PI), and to investigate the relationship between the severity of insomnia and these changes.Methods A case-control study was performed among 40 patients diagnosed with PI according to International Classification of Diseases-10 and 50 disease-free controls. Pittsburgh Sleep Quality Index (PSQI), Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD), WHO-UCLA auditory verbal learning test, and cancellation test were used to evaluate the neuropsychology and cognitive ability of all patients. Statistical analysis was performed on the results of these tests.Results The PSQI, HAMA, and HAMD scores of the PI group were higher than those of the control group, while the scores of verbal learning and cancellation tests were lower in the PI group (P<0.05). In the PI group, the decline in sleep quality was positively correlated with anxiety (r=0.350); a linear relationship was found between sleep quality and the following factors: degree of education, course of disease, and HAMD score (α= 0.1, F=13.44, P<0.05). Regression analysis was performed to find factors that affect cognitive ability; sleep quality and HAMA score were both significantly correlated with the cognitive ability (α=0.1, F=12.943, P<0.05).Conclusions PI patients suffer decline in sleep quality and cognitive ability and show obvious depression and anxiety. Decline in sleep quality is significantly correlated with anxiety. Decline in sleep quality may reduce cognitive ability.