Background <p>Hypothyroidism is one of the most common endocrine disorders in dogs, that is caused by reduction in thyroxine hormone production.</p> Objectives <p>This study aimed to detect the incidence of clinical hypothyroidism among cases suffering from dermatological changes or obesity, investigate the complications in severely affected hypothyroid dogs and evaluate the response to levothyroxine treatment.</p> Method <p>Total number of 212 dogs of different ages, breeds and of both sexes were included in this study, where 200 dogs were suffering from alopecia or obesity, the other 12 healthy dogs were used as control group.</p> Results <p>After ruling out other causes of alopecia and obesity, hypothyroidism was diagnosed in 28 dogs (14%) depending on the result of thyroid function test. Results of this study showed that the highest incidence of hypothyroidism was reported in Golden retriever (21.42%) followed by Griffon dogs (17.85%). Additionally, hypothyroidism was mostly reported in middle-aged dogs (60.71%) of different breeds. Males (57.14%) revealed higher incidence than females. The hypothyroid dogs showed a wide range of clinical signs including dermatological, metabolic, psychological alterations in addition to cardiovascular, respiratory, neuromuscular, gastrointestinal and gynecological abnormalities. Radiography revealed pulmonary edema in dogs affected with heart problems (<i>N</i> = 2), dilated esophagus in hypothyroid dogs showing vomiting (<i>N</i> = 2). Echocardiographic examination of hypothyroid dogs with heart problems revealed first grade diastolic dysfunction. Treatment with levothyroxine induced clinical improvement within one month of administration.</p> Conclusion <p>Hypothyroidism is a relatively common condition in dogs compared to other diseases causing dermatological changes or obesity in dogs. Therefore, it must be considered for early diagnosis and treatment before encountering complications that could be life threatening for dogs.</p>