Background In chest computed tomography (CT), iterative reconstruction (IR) algorithms maintain diagnostic image quality (IQ) while significantly reducing the dose. Purpose To evaluate the impact of IR on IQ of chest CT at effective doses below 0.3 mSv. Material and Methods Twenty chest CT scans performed at effective dose below 0.3 mSv (CT1) were reconstructed varying three parameters: filtered back-projection and IR iDose⁴ algorithms; 512 × 512 and 768 × 768 matrices; and sharp and soft kernels, thus generating eight series per patient. The qualitative evaluation of the IQ was performed by ranking series from 1 to 8 (8 corresponding to the highest rank) which was subsequently compared to quantitative assessment of IQ by using an appropriated merit formula. Intra- and inter-reader IQ ranking reliability was also evaluated using Cohen’s kappa. Analysis of lung findings was finally compared between the best CT1 series and the reference CT (CT0). Results The best series in terms of qualitative and quantitative IQ was obtained using IR, 512² matrix and soft kernel. The best CT1 series detected nodules greater than 4 mm with an almost perfect match with CT0. Conclusion Chest CT performed at effective doses below 0.3 mSv may be used to confidently diagnose lesions greater than 4 mm using iDose⁴, soft kernel and 512 × 512 matrix.