Genital Herpes: This is often the first consideration due to its prevalence and the characteristic presentation of painful ulcers. The diagnosis can be confirmed with viral culture, PCR, or serology.

Syphilis (Primary): The primary stage of syphilis classically presents with a single, painless chancre, but multiple ulcers can occur. Diagnosis is through darkfield microscopy, serology, or nucleic acid amplification tests.
Chancroid: Caused by Haemophilus ducreyi, chancroid presents with one or more painful ulcers and is often accompanied by lymphadenopathy. Diagnosis is clinical, with confirmation by culture or PCR.
Lymphogranuloma Venereum (LGV): Although LGV typically presents with a small, painless lesion that may go unnoticed, followed by lymphadenopathy, it can cause ulcers in some cases. Diagnosis is through serology or nucleic acid amplification tests.

Squamous Cell Carcinoma: Although rare, any non-healing ulcer in the genital area should prompt a biopsy to rule out squamous cell carcinoma, especially in uncircumcised men or those with a history of HPV infection.
Behçet's Disease: A form of vasculitis that can cause genital ulcers, among other symptoms. It's crucial to consider this diagnosis due to its systemic implications and the need for early treatment.

Granuloma Inguinale (Donovanosis): Caused by Klebsiella granulomatis, this condition presents with painless, beefy-red ulcers that bleed easily. It's more common in tropical and subtropical regions.
Fixed Drug Eruption: A condition that can cause ulcers in response to certain medications. The ulcers typically recur at the same site each time the offending drug is taken.
Erythema Multiforme: An immune-mediated condition that can cause targetoid lesions and, less commonly, ulcers, often in response to infections or medications.