Drug induced aseptic meningitis is a rare but challenging diagnosis, most commonly reported with nonsteroidal anti-inflammatory drugs and antibiotics. Trimethoprim/sulfamethoxazole is a sulfonamide that is widely used in clinical practice for the treatment and prophylaxis of various infections. Drug induced aseptic meningitis, when seen with trimethoprim/sulfamethoxazole, occurs predominantly in patients with some degree of immune compromise and is less commonly seen in immune competent individuals. The patient often exhibits the classic symptoms of meningitis. Early diagnosis is important, since the cessation of the antibiotic leads to rapid clinical improvement. Trimethoprim/sulfamethoxazole induced aseptic meningitis has been underreported to FDA/MED-WATCH program. Here we report two cases of trimethoprim/sulfamethoxazole: an immune competent individual and immune compromised individual, both of which presented with signs of meningitis and a negative infectious workup. Trimethoprim/sulfamethoxazole is an uncommon and mysterious adverse reaction to a commonly used antibiotic. It should be considered in the differential diagnosis of patients presenting with acute signs and symptoms of meningitis especially after infectious causes have been ruled out.