A hydrocele (HI-droe-seel) is a fluid-filled sac surrounding a testicle that causes swelling in the scrotum. Hydrocele is common in newborns and usually disappears without treatment during the first year of life. Older boys and adult men can develop a hydrocele due to inflammation or injury within the scrotum. A hydrocele usually isn't painful or harmful and might not need any treatment. But if you have scrotal swelling, see your doctor to rule out other causes. Symptoms. Usually, the only indication of a hydrocele is a painless swelling of one or both testicles. Adult men with a hydrocele might experience discomfort from the heaviness of a swollen scrotum.