For most children, the inability to urinate is caused by dehydration. Common causes of dehydration are not drinking enough fluids, diarrhea, vomiting, and fever. A child can also quickly become dehydrated in hot weather.

When a child is not dehydrated, the inability to urinate can be caused by:

• Injury.
• Infection.
• Medicines, such as Actifed, Benadryl, Chlor-Trimeton, Dimetapp, Robitussin Cough and Cold, or Tavist.
• Problems with the structure or function of the urinary tract, such as vesicoureteral reflux, an obstruction in the urinary tract, or another abnormality.

A child who is not dehydrated but cannot urinate should be evaluated by a health professional. If the bladder fills up, the child will be very uncomfortable.