**Core Concept:** Genital tuberculosis (TB) is a sexually transmitted infection caused by the Mycobacterium tuberculosis complex bacteria. It can affect various reproductive organs like the uterus, fallopian tubes, and ovaries. After complete treatment, the risk of complications depends on the extent of organ involvement and the individual's immune status.

**Why the Correct Answer is Right:** The correct answer is **C. Pelvic Inflammatory Disease (PID)**. Pelvic inflammatory disease is a severe complication of uncontrolled genital tuberculosis. It occurs when the infection spreads beyond the genital tract, affecting the fallopian tubes, uterus, and surrounding structures. The inflammation can lead to tubal obstruction, peritonitis, and potentially infertility or ectopic pregnancy.

**Why Each Wrong Option is Incorrect:**

A. **Endometritis:** This is the inflammation of the uterine lining (endometrium) caused by genital TB. It is a less severe complication and does not usually progress to PID.

B. **Ovarian cyst:** Although genital TB can cause cysts, it is not the commonest complication after complete treatment. PID is more likely to occur due to the spread of infection beyond the ovaries.

D. **Tubal peritonitis:** Peritonitis is a possible complication of PID but is not the correct answer as PID is the commonest complication of genital TB after complete treatment.

**Clinical Pearl:** Incomplete treatment or reinfection can lead to recurrent genital TB and its complications. Regular follow-up with appropriate antibiotics can prevent such complications.

**Correct Answer:** C. Pelvic Inflammatory Disease (PID) is the commonest complication of genital tuberculosis after complete treatment due to the spread of infection beyond the genital tract and the potential for tubal obstruction, peritonitis, and ectopic pregnancy.