Reversed halo sign (RHS) is often seen in computed tomography (CT) scans of cryptogenic organizing pneumonia (COP). To investigate its clinical features, we retrospectively reviewed 30 cases of COP in 13 men and 17 women, whose age range 28 to 73, with a mean of 58.4 years. All diagnoses were made with transbronchial lung biopsy (TBLB), but it took an average of 24.8 days from the first visit until the diagnosis of COP. RHS was seen in 7 cases (23%) and multiple RHSs were seen in 3 cases. We treated 5 cases (71%) with steroids. Their CT images showed parenchymal abnormalities which started as nodular lesions, then enlarged, and then the central lesion changed into ground-glass opacities, until finally, RHS was formed. The presence of RHS does not necessarily indicate a marked difference in the clinical course of COP. In conclusion, in the present series RHS was a phase of the clinical course of COP, and was useful to diagnose COP.