Aim of the work: a descriptive study including analysis of HRCT chest done for patients known to have collagen diseases for diagnosis and classification of interstitial lung diseases. Patients and methods: forty five patients were included in our study (23 rheumatoid arthritis, 14 systemic lupus erythematosis and 8 scleroderma). This was a retrospective study that included patients with collagen diseases either outpatients or referred from the Rheumatology Departement at Ain Shams University Hospitals to the Radiodiagnosis Department for HRCT chest examination. HRCT chest images were interpreted for identification of lung interstitium architectural abnormalities associated with collagen diseases and they were statistically analyzed. Results: The mean age of the selected patients was about 42 years old. Parenchymal involvement was noted in 30 cases that represented 66.6% of included cases in the study, 15 cases had normal HRCT of the chest representing 33.4% of the cases. Conclusion: HRCT of the chest has a reasonable role in the diagnosis of interstitial lung diseases and has the ability to be classify according to the pattern of involvement, distribution and extent of the disease as well as to estimate the severity and help in prognosis of the disease process.