<b><i>Background and Purpose:</i></b> Craniocervical fibromuscular dysplasia (FMD) is associated with dissections and with S-shaped curves in the internal carotid artery (ICA). We evaluated the occurrence of S-curves in patients presenting with acute strokes due to ICA steno-occlusive dissections. <b><i>Methods:</i></b> This was a retrospective review of the interventional databases of two academic tertiary-care institutions. The presence of ICA S-shaped curves, C-shaped curves, 360-degree loops, as well as classic FMD and atherosclerotic changes at the ICA bulb and curve/loop was determined. Cases of carotid dissections were compared with a control group (consecutive non-tandem anterior circulation strokes). <b><i>Results:</i></b> Twenty-four patients with carotid dissections were compared to 92 controls. Baseline characteristics and procedural variables were similar, with the exception of younger age, less frequent history of hypertension, diabetes, atrial fibrillation and stent retriever use in patients with dissections. The rates of mTICI2b-3 reperfusion, parenchymal hematoma, good outcome and mortality were similar amongst groups. The frequency of S-curves (any side without superimposed atherosclerosis) was 29% in the dissection group versus 7% in controls (p < 0.01). S-curves were typically mirror images within the dissection group (85% had bilateral occurrence). The frequency of C-shaped and 360-degree curves was similar between groups. FMD changes within the craniocervical arteries were statistically more common in dissection patients. Ten patients (41%) of the dissection group had S-curves or classic FMD changes. Multivariate analysis indicated that S-curves were independently associated with the presence of dissections. <b><i>Conclusion:</i></b> S-shaped ICA curves are predictably bilateral, highly associated with carotid dissections in patients with moderate to severe strokes, and may suggest an underlying presence of FMD.