The risk of insufficiency fractures at the iliac crest following pin insertion during robot-assisted total hip arthroplasty (THA) is unknown, as there have been very few reports on this complication. Here, we report two cases of insufficiency fractures of the contralateral iliac crest following robot-assisted THA using the Mako system (Stryker Orthopaedics, Mahwah, NJ, USA). Both patients underwent left THA using the anterolateral supine approach, and three threaded bone pins (4.0 mm diameter) were inserted into the right iliac crest for pelvic array fixation. In case one, all three pins achieved bicortical fixation. In case two, one pin demonstrated long transcortical fixation with the outer cortex of the ilium, another was inserted into soft tissue, and the third pin was fixed monocortically. Postoperatively, both patients were discharged without pain or radiographic evidence of fracture; however, contralateral iliac pain developed approximately four weeks postoperatively without trauma. Insufficiency fractures of the iliac crest at the pin insertion sites were confirmed by plain radiography. Bone union was observed within three to six months of conservative treatment in both cases, with T-cane ambulation and no weight-bearing restrictions. These cases suggest that both bicortical and transcortical pin fixation to the iliac crest may cause insufficiency fractures of the iliac bone. This report highlights the need for increasing awareness of insufficiency fractures associated with pin insertion in robot-assisted THA.