Late-onset retroperitoneal hemorrhage from renal intraparenchymal pseudoaneurysm (RIP) following a kidney biopsy is an extremely rare complication but should not be ignored, especially in high-risk populations. Here, we introduce a 32-year-old Caucasian female who presented with sudden-onset left-sided flank pain. She had recently been diagnosed with systemic lupus erythematosus (SLE) and had undergone a computed tomography (CT)-guided core needle biopsy of the left kidney 9 days earlier. The results were consistent with lupus nephritis class III or IV. Initial vitals were within normal limits. She appeared pale and her left flank was tender to palpation without discoloration or abdominal distention. Laboratory investigations showed a hemoglobin level of 7.1 g/dL. The CT scan of the abdomen and pelvis revealed a large hyperdense left perinephric collection consistent with perinephric hematoma with a moderate amount of retroperitoneal stranding most prominent on the left side extending across the midline to the right side. Contrast extravasation was suspected in the lower pole of the left kidney consistent with active bleeding site. Emergent renal angiography revealed a 2 × 1 cm intraparenchymal pseudoaneurysm in the lower pole of the left kidney along with a few small microaneurysms. Coil embolization of the pseudoaneurysm was successfully performed without any complications. In conclusion, SLE or lupus nephritis in this patient may be the predisposing factors for microaneurysm and RIP formations. RIP is an unusual complication after percutaneous kidney biopsy that carries a significant mortality rate if ruptured, causing retroperitoneal hemorrhage. Clinicians should be vigilant when encountering high-risk patients with persistent hematuria, flank pain, or abdominal pain within four weeks after a kidney biopsy.