With increasing use of iliocaval stenting, complications of such stenting have also become more common. In-stent restenosis (ISR), an outcome that is responsible for a majority of reinterventions, is one that has not been studied in detail. Characteristics of ISR in addition to outcomes after reintervention are evaluated. A retrospective review of contemporaneously entered electronic medical record data on 372 limbs with initial unilateral iliocaval stents (247 left and 125 right) placed during a 3-year period from 2015 to 2017 was performed. ISR was estimated from stent and flow channel diameters measured using duplex ultrasound. Characteristics evaluated included onset of ISR after stent placement and progression over time. Regression analysis was performed to evaluate risk factors for development of ISR. Outcomes after reintervention for ISR were also appraised. Kaplan-Meier analysis was used to assess stent patency afater intervention; paired t-test was used to examine preintervention and postintervention outcomes. There were 361 limbs that underwent stenting for stenotic lesions, whereas 11 underwent stenting for chronic native vein occlusions. ISR was noted as early as postintervention day 1. It progressed to a maximal value by 6 months and stabilized thereafter. The overall median ISR across stented common femoral, external iliac, and common iliac segments at 12 months was 43.75%. The segment most commonly affected by ISR was the external iliac vein (77.5%). Up to 89% of stents can have some degree of ISR at 12 months. Variables evaluated as predictors for ISR included age, sex, thrombophilia, thrombotic or nonthrombotic lesion, inflow, stent compression, shear rate, and flow rate. Of these, only lack of stent compression was a significant predictor of ISR at 6 and 12 months. During a median follow-up of 13 months, 50 of 372 (13%) limbs underwent reintervention for ISR and 12 (3%) underwent reintervention for stent occlusion (8 acute [<30 days] and 4 chronic [>30 days]). After reintervention, the Venous Clinical Severity Score improved from 6 to 4 for the ISR cohort (P < .001). Median primary, primary assisted, and secondary patencies after reintervention for ISR were 37, 38, and 17 months, respectively. ISR occurs early after iliocaval stenting but stabilizes around 6 months. Progression of ISR to stent occlusion is rare. No statistically significant, modifiable predictor for ISR was noted. After reintervention for ISR, good clinical outcomes and stent patencies can be expected.