Objectives The aim of this study was to find the prevalence of insomnia among people aged over 65 years, attending primary care settings, in a semi-rural area of Kavala, in northern Greece, to investigate the possible associated factors (demographic, psychological, medical) and to find the possible correlation of insomnia with a general sense of health. Methods Two groups of people attending primary care settings (open centre for the elderly and old people's home) and aged over 65 years were studied, with a total sample size of 201. The presence of insomnia was assessed by the ICD-10 criteria, a medical and psychiatric history was taken and the validated Greek version of the 28-point General Health Questionnaire (GHQ-28) was used. The data were analysed by Pearson's chi-square and Student's t-test and multiple regression analysis. Results The prevalence of insomnia was 42.78%. Factors that correlated with insomnia were chronic obstructive pulmonary disease, diabetes, cardiovascular disorders, prostate diseases, arthritis, dementia, and consumption of bronchodilators, non-steroidal anti-inflammatory drugs and anxiolytics. No demographic factors were associated with insomnia. In the GHQ-28, people with insomnia had a pathological mean score, while those with normal sleep scored below the cut-off point. Conclusion The prevalence of insomnia is significantly higher among the elderly than in the general population. Organic diseases and consumption of certain medications and anxiolytics seemed to be associated with insomnia in the present study. Psychiatric disorders are surprisingly not correlated with the presence of insomnia, while the high GHQ-28 score of those people with insomnia reveals a connection to their poor health status. Moreover, the results imply that benzodiazepine consumption does not alleviate insomnia and a thorough clinical examination of the patient is needed before treatment is decided.