• Aspergillosis
• Avian influenza (bird flu)
• Blackhead disease
• Botulism
• Cage Layer Fatigue
• Coccidiosis
• Colds
• Crop bound
• Egg bound
• Erysipelas
• Fatty Liver Hemorrhagic Syndrome
• Fowl Cholera
• Fowl pox
• Fowl Typhoid
• Gapeworms
• Infectious Bronchitis
• Infectious Bursal Disease (Gumboro)
• Infectious Coryza
• Lymphoid Leucosis
• Marek's disease
• Moniliasis
• Mycoplasmas
• Newcastle disease
• Necrotic Enteritis
• Omphalitis (Mushy chick disease)
• Psittacosis
• Pullorum (Salmonella)
• Scaly leg
• Squamous cell carcinoma
• Tibial dyschondroplasia
• Toxoplasmosis
• Ulcerative Enteritis

Chickens are also susceptible to parasites, including lice, mites, ticks, fleas, and intestinal Worms.

Chickenpox is a disease of humans, not chickens.