Non-classic congenital adrenal hyperplasia (NCAH): This condition is often mistaken for PCOS due to similar symptoms such as hyperandrogenism, irregular menstrual cycles, and infertility. The similarity in clinical presentation makes NCAH a common differential diagnosis for PCOS.

Thyroid dysfunction: Both hypothyroidism and hyperthyroidism can cause menstrual irregularities and are often seen in conjunction with PCOS or can mimic its symptoms.
Hyperprolactinemia: Elevated prolactin levels can lead to menstrual irregularities, galactorrhea, and infertility, overlapping with PCOS symptoms.
Cushing's syndrome: This condition, characterized by excess cortisol, can cause weight gain, hirsutism, and menstrual irregularities, similar to PCOS.
Androgen-secreting tumors: Ovarian or adrenal tumors secreting androgens can mimic the hyperandrogenic symptoms of PCOS.

Pituitary adenoma: Although less common, a pituitary adenoma can cause hyperprolactinemia or disrupt other hormonal balances, leading to symptoms that mimic PCOS. Missing this diagnosis could lead to significant morbidity due to the potential for the tumor to affect vision or lead to other serious complications.
Adrenal carcinoma: A rare but potentially life-threatening condition that can cause virilization and other symptoms overlapping with PCOS. Early detection is crucial for treatment and prognosis.

Gonadal dysgenesis: Conditions such as Swyer syndrome can present with hypergonadotropic hypogonadism and may mimic some aspects of PCOS, particularly in terms of ovarian dysfunction.
Steroidogenic enzyme deficiencies: Rare genetic disorders affecting steroid hormone production can lead to symptoms that might be confused with PCOS, such as congenital adrenal hyperplasia due to 11-beta hydroxylase deficiency.
Insulin resistance syndromes: Rare syndromes like Rabson-Mendenhall syndrome or type A insulin resistance can present with severe insulin resistance and hyperandrogenism, mimicking PCOS.