what are the common diseases associated with this gland?
Graves' disease, Thyroid nodules,  goitre, cancer, etc.
Thyroid
Graves' disease is an autoimmune disorder that is the most common cause of hyperthyroidism. 
where is thyroid gland situated in human body Neck what does this gland do? The primary function is the production of the iodine-containing thyroid hormones, triiodothyronine (T) and thyroxine (T) and the peptide hormone calcitonin.
wiki:19590201
Thyroid [SEP] Graves' disease
Graves' disease is an autoimmune disorder that is the most common cause of hyperthyroidism. In Graves' disease, for an unknown reason autoantibodies develop against the thyroid stimulating hormone receptor. These antibodies activate the receptor, leading to development of a goitre and symptoms of hyperthyroidism, such as heat intolerance, weight loss, diarrhoea and palpitations. Occasionally such antibodies block but do not activate the receptor, leading to symptoms associated with hypothyroidism. In addition, gradual protrusion of the eyes may occur, called Graves' ophthalmopathy, as may swelling of the front of the shins. Graves' disease can be diagnosed by the presence of pathomnomonic features such as involvement of the eyes and shins, or isolation of autoantibodies, or by results of a radiolabelled uptake scan.