Blood blister-like aneurysms (BBAs) were considered a therapeutic challenge for both microsurgeons and endovascular therapists. While a great deal of efforts had been put to refining the treatment of BBAs, the diagnostic criteria had not been established yet. In this study, we reviewed data of 43 suspicious, small (<1cm), broad-necked aneurysms at supraclinoid segment of internal carotid artery (ICA) in 41 patients who had been treated with microsurgery in our hospital during the past 5years. Diagnosis of BBAs and non-blister aneurysms was based on intraoperative findings. Epidemiological, clinical, and radiological features of BBAs and non-blister aneurysms were compared. Subtypes of BBAs were also compared. Discriminant analysis was used to generate a differentiating model for BBAs. Seventeen aneurysms were diagnosed as BBAs and 26 were diagnosed as non-blister aneurysms. No significant difference regarding age, gender, association of multiple aneurysms, or location on ICA was found between the groups. Dome/neck ratio and distal angle (intersection angle of aneurysm with ICA, distal to ophthalmic artery branching site) of BBAs were smaller than those of non-blister aneurysms (P=0.009 and P=0.002). A discriminant function including aforementioned factors with an overall accuracy of 76.2% was yielded (P=0.005). BBAs and non-blister aneurysms were difficult to differentiate by clinical and radiological features as they share many characteristics in common. Dome/neck ratio <1 did not guarantee accurate diagnosis of BBAs. A discriminant function incorporating dome/neck ratio and degree of distal angle as factors might increase the accuracy of pre-surgical diagnosis of BBAs.