Diabetes is associated with:

• Cystic Fibrosis
• Autism
  
• Celiac Disease
• Hypothyroidism
• Down syndrome
• Turner syndrome
• Klinefelter syndrome
• Wolfram syndrome
• Friedreich ataxia
• Prader–Willi syndrome
• Bardet–Biedl syndrome
• Myotonic dystrophy

sources:

Brook C, Clayton P, Brown R. Brook's Clinical Pediatric Endocrinology, 5th Edition. Malden Massachusetts, Blackwell Publishing; 2005:437

Freeman SJ, Roberts W, Daneman D. Type 1 diabetes and autism: is there a link? Diabetes Care. 2005 Apr;28(4):925-6