To determine the patterns of thyroid dysfunction and autoantibodies associated with SLE and RA patients, twenty patients with SLE and another group of twenty with RA were studied. The results were compared with those of twenty apparently healthy age- and sex- matched controls. All patients were subjected to complete history taking, thorough clinical examination and joint examination. All patients and controls were subjected to the following investigations: T3, T4, TSH, antithyroglobulin antibodies (ATGAb) and thyroid peroxidase antibodies (TPOAb). Also, complete blood picture, ESR, RF, ANA, CRP and LE cells were done. This study revealed that thyroid disorders were significantly increased in SLE patients (50%) when compared to RA (15%) (P<0.05). In SLE group, 20% had euthyroid sick syndrome, 20% had hypothyroidism (10% subclinical and 10% biochemical), and 10% had hyperthyroidism (5% subclinical and 5% biochemical). However, in RA, 10% had hypothyroidism (subclinical) and 5% had subclinical hyperthyroidism. TPOAb was found in 15% of SLE and 5% of RA patients and 10% of controls, but the titres were higher in SLE and RA patients. Also, ATGAb was found in 5% of SLE, 30% of RA patients and 10% of controls, but the titres were higher in SLE and RA patients. It is concluded that thyroid abnormalities are more implicated with euthyroid sick syndrome and hypothyroidism (subclinical and overt) than hyperthyroidism in SLE patients. SLE and RA were associated with antithyroid antibodies (TPOAb in SLE and ATGAb in RA). Performance of thyroid function tests in patients with SLE, in particular and RA as a part of the biochemical and immunological profiles, may help in early detection of associated thyroid disorders.