The objective of the present study was to determine the prevalence of Demodex sp among patients with cancer, on hemodialysis and diabetes mellitus and among controls in order to investigate if there are significance differences in Demodex sp positivity. The study was conducted at Ataturk University Research and Application Hospital, Turkey and the Yuzuncu Yil University Parasitology Laboratory, Turkey between 22 August 2011 and 31 May 2016. Study subjects consisted of 50 patients with cancer, 50 patients diagnosed with chronic renal failure and were on hemodialysis, 50 patients with diabetes mellitus and 75 healthy controls. Each patient and each control had a skin surface biopsy using a slide with cyanoacrylate applied wet to the skin until it dried and then was removed and examined under light microscopy at x10 and x40 magnification. A positive sample was one in which mites / 1 cm(2) of skin were identified. Twenty percent of the total patient group (n=150) and 5.3% of the control group (n=75) had a positive result. Among the patient groups, 26% of cancer patients, 22% of diabetes mellitus patients and 12% of patients on hemodialysis were positive. A significant association was seen between a positive skin biopsy for Demodex sp and cancer (p<0.01) and between a positive biopsy and diabetes mellitus (p<0.01). In conclusion, patients with cancer and diabetes mellitus are more likely to have a positive skin biopsy for Demodex sp than controls.