A man has been arrested on suspicion of rape following an incident in the town centre.
Sussex Police said it was investigating an incident reported to have occurred in the vicinity of Sparks Court, Littlehampton, at around 3am on Saturday.
According to eyewitnesses, the area was cordoned off with police tape.
Police said a 24-year-old local man was arrested on suspicion of rape.
He has been released on conditional bail until July 22, pending further enquiries, police said.
Officers have engaged with the victim, a local man in his 20s, and provided support, and the investigation is ongoing, police said.
On the Sussex Police website, there is advice and guidance for victims of rape and contact details for charities that offer support.