The first hints of the illness are usually mild, intermittent, and show up on just one side of the body. Three cardinal signs are:

• Shakiness, from a tremor in a hand, arm, or leg or the jaw or face when the patient isn't actively moving.
  
• Stiffness, or rigidity of the arms, legs, and torso.
  
• Slowness of movements, also known as bradykinesia.

Other common signs and symptoms include:

• Small, cramped handwriting.
  
• A stooped posture.
  
• Less arm-swinging than before while walking.
  
• A blank, "masklike" facial expression.

As the disorder progresses, additional problems may grow more significant, including:

• Problems with balance and falling.
  
• Walking with small, shuffling steps.
  
• Moments of "freezing" when the patient's feet suddenly can't move forward.
  
• Difficulty swallowing.
  
• A weak and muffled voice.