Genital Herpes: Given the patient's immunocompromised status due to HIV, genital herpes is a common and likely diagnosis. The lesions are typically painful, multiple, and can be found on the penis, scrotum, or around the anus.

Syphilis: This sexually transmitted infection can cause a variety of lesions, including the characteristic chancre of primary syphilis, which is a painless ulcer. In HIV patients, syphilis can have atypical presentations.
Human Papillomavirus (HPV) related lesions: HPV can cause a range of lesions from condyloma acuminata (genital warts) to more severe lesions that can progress to penile cancer. Immunocompromised patients are at higher risk for persistent HPV infection and its consequences.
Molluscum Contagiosum: This viral infection causes small, pearly, or flesh-colored lesions. In immunocompromised patients, the lesions can be larger and more numerous.

Squamous Cell Carcinoma: Although less common, penile cancer is a critical diagnosis not to miss, especially in HIV patients who may have a higher risk due to HPV infection. Early detection is crucial for treatment and prognosis.
Lymphogranuloma Venereum (LGV): This is another sexually transmitted infection caused by certain types of Chlamydia trachomatis. It can cause lesions, but more importantly, it can lead to significant lymphadenopathy and other systemic symptoms if not treated promptly.

Kaposi's Sarcoma: This is a type of cancer that can cause lesions on the skin, including the penis, and is more common in immunocompromised patients, especially those with advanced HIV disease.
Basal Cell Carcinoma or other skin cancers: While less common on the penis, these skin cancers can occur and should be considered, especially in patients with risk factors such as fair skin or a history of sun exposure.
Donovanosis (Granuloma Inguinale): A rare sexually transmitted infection caused by Klebsiella granulomatis, characterized by genital ulcers that are typically painless and bleed easily on contact.