Delayed cerebral ischemia (DCI) is an important cause of poor outcome after 
aneurysmal subarachnoid hemorrhage (SAH). We studied differences in incidence 
and impact of DCI as defined clinically after coiling and after clipping in the 
International Subarachnoid Aneurysm Trial. We calculated odds ratios (OR) for 
DCI for clipping versus coiling with logistic regression analysis. With coiled 
patients without DCI as the reference group, we calculated ORs for poor outcome 
at 2 months and 1 year for coiled patients with DCI and for clipped patients 
without, and with DCI. With these ORs, we calculated relative excess risk due to 
Interaction (RERI). Clipping increased the risk of DCI compared to coiling in 
the 2,143 patients OR 1.24, 95% confidence interval (95% CI 1.01-1.51). Coiled 
patients with DCI, clipped patients without DCI, and clipped patients with DCI 
all had higher risks of poor outcome than coiled patients without DCI. Clipping 
and DCI showed no interaction for poor outcome at 2 months: RERI 0.12 (95% CI 
-1.16 to 1.40) or 1 year: RERI -0.48 (95% CI -1.69 to 0.74). Only for patients 
treated within 4 days, coiling and DCI was associated with a poorer outcome at 
1 year than clipping and DCI (RERI -2.02, 95% CI -3.97 to -0.08). DCI was more 
common after clipping than after coiling in SAH patients in ISAT. Impact of DCI 
on poor outcome did not differ between clipped and coiled patients, except for 
patients treated within 4 days, in whom DCI resulted more often in poor outcome 
after coiling than after clipping.