The latest advice from the Uganda immigration service is the following:

• Nationals of USA, the European Union and Japan require a tourist visa and should apply in advance of travel to Uganda. The visa fee of $50 is payable upon arrival at any Uganda entry point or during an online application.
• Uganda tourist visas are NOT required by nationals of Ireland, the East Africa community, COMESA. Other nationals should check the Uganda immigration website.
• Applications for all Ugandan visas should be made online on the Uganda immigration website.
• A single entry visa to Uganda costs US$ 50 and is valid for between two weeks and three months.