**Core Concept:** Renal transplantation is a common treatment option for end-stage renal disease, with immunosuppressive medications used to prevent organ rejection. However, transplant recipients are at risk of various complications due to these immunosuppressive drugs and other factors.

**Why the Correct Answer is Right:** The correct answer is **C. Vascular Thrombosis**. In renal transplantation, the risk of vascular thrombosis is primarily due to the use of immunosuppressive medications, particularly calcineurin inhibitors like cyclosporine or tacrolimus. These drugs suppress the immune system, making the patient susceptible to infections and malignancies. Additionally, they can impair the endothelium, leading to hypercoagulability and increased risk of thrombosis.

**Why Each Wrong Option is Incorrect:**

A. **Cardiovascular Disease (VD)**: This is not the principal cause of death in renal transplant patients, though they are at higher risk due to immunosuppression.

B. **Infections (INF)**: While infections are a concern in renal transplant recipients, they are not the primary cause of death.

D. **Neoplasms (N)**: Solid cancers are more common in transplant patients, but they are not the primary cause of death in this context.

**Clinical Pearl:** The primary cause of death in renal transplant patients is **Vascular Thrombosis (VD)**, particularly in the early post-transplant period. This emphasizes the importance of close monitoring and prophylactic measures to prevent thrombotic complications.

**Correct Answer: C. Vascular Thrombosis**