Background: In adults, unilateral facial thickening carries a wide differential including congenital, neoplastic, inflammatory, autoimmune, endocrine, and fibro-osseous causes. Early on, several of these can mimic an autoimmune connective tissue disease, making diagnosis a real challenge in rheumatology. We report a case highlighting the diagnostic overlap between Parry–Romberg syndrome and morphea. Case description: A 28-year-old woman presented with left-sided facial changes progressing over approximately 1.5 years, beginning with edema and erythema of the left hemiface for roughly five months, followed by progressive volume loss of the nasolabial region and upper lip (Figure 1). She reported intermittent facial paresthesias but no Raynaud's phenomenon, digital ulcers, dysphagia, arthritis, seizures, focal deficits, or visual symptoms, and no contralateral facial/limb atrophy, dental/oral changes, prior trauma, or congenital asymmetry. History included asthma, prior smoking, a family history of psoriasis, and recent travel before onset. Examination showed clear left hemifacial asymmetry with soft tissue atrophy of the nasolabial fold and upper lip, no sclerodactyly or arthritis, and normal neurological exam. Antinuclear antibodies were low-titre (1:160, speckled) with negative ENA; inflammatory markers, muscle enzymes, and infectious workup were unremarkable. Brain MRI showed only an incidental, nonspecific white matter lesion. Skin biopsy (Figure 2) revealed epidermal atrophy, a perivascular lymphoplasmacytic infiltrate, and dermal/hypodermal fibrosis. Deep hypodermal involvement, upward displacement of adnexal structures, and absence of marked dermal sclerosis favoured Parry–Romberg syndrome over linear scleroderma. She started methotrexate 10 mg/week with folic acid; at follow-up, disease activity had stabilised, with reconstructive treatment (autologous fat grafting, Coleman technique) planned after further confirmed stability. Discussion/Conclusions: Parry–Romberg syndrome follows a biphasic course—an inflammatory phase mimicking autoimmune disease, followed by progressive atrophy—making early misclassification common. Biopsy was key to distinguishing it from morphea, which typically shows dense dermal sclerosis with hyalinized collagen. Clinicians should consider Parry–Romberg syndrome in the differential of progressive unilateral facial changes and pursue early biopsy, since its atrophic phase can closely overlap with morphea both clinically and histologically.