Objective: Our aim was to study whether recovery from a Raynaud?s attack and involvement of the thumb are differentiators for systemic sclerosis (SSc) in patients with Raynaud?s phenomenon (RP). Method: A stepwise cooling and recovery procedure was performed, provoking an RP attack, in patients with primary Raynaud?s phenomenon (PRP, n =?68) and SSc (n?=?18). During the procedure, the perfusion of all five fingers during cooling and recovery was assessed by photoelectric plethysmography. Results: In SSc patients, perfusion after 10?min in one or more fingers was more frequently not restored than in PRP patients (p?=?0.001), with a negative predictive value of 98%. The thumb was more frequently involved in SSc patients (p?=?0.036), with a negative predictive value of 95%. Positive predictive values were low. Conclusions: In patients with RP, when there is restoration of perfusion in all fingers after 10?min or when the thumb is spared, the presence of an underlying SSc is very unlikely. Although these results need to be validated in a clinical setting in a larger prospective study, these signs can help physicians to select additional testing for SSc in RP patients.