<b><i>Introduction:</i></b> Lenvatinib (LEN) is a multitarget tyrosine kinase inhibitor currently used for advanced, radioiodine refractory differentiated thyroid cancer (RAI-R DTC). Among adverse events (AEs), nausea, vomiting, and decreased appetite have been frequently described. We aimed to evaluate the prevalence, the clinical presentation, and the effectiveness of conservative treatment of gallbladder disorders in a consecutive series of patient treated with LEN. <b><i>Methods:</i></b> Patients with RAI-R DTC experiencing clinical symptoms suggestive for gallbladder disorders during LEN treatment were evaluated with laboratory investigations and contrast-enhanced abdominal computed tomography (CT) and ultrasound scan (US). <b><i>Results:</i></b> After a median time of 2 months from the start of treatment, 5/13 patients (38.4%) complained of gastrointestinal symptoms, with increased biliary enzymes levels, especially γGT, and CT/US suggestive of acute cholecystitis (AC). The onset of symptoms and the peak of γGT levels frequently corresponded to the highest reduction in body weight during the first months of treatment. All patients were treated with supportive care and, when appropriate, with ursodeoxycholic acid; in 4 patients, LEN dose reduction or short interruption was needed, too. <b><i>Conclusions:</i></b> In patients with RAI-R DTC treated with LEN, a high prevalence of AC in the first months of treatment was documented. Mainly due to the low specificity of symptoms such as anorexia, nausea, and vomiting, this AE is likely to be frequently misdiagnosed. The onset of the disease was associated to the weight loss observed during the first months of treatment and contributes to further decrease in body weight. Therefore, particularly during the first months of treatment, or at any time of huge reduction of body weight, monitoring of γGT and US is crucial for prompt diagnosis and treatment. Conservative medical treatment and LEN dosage titration, together with dietary and rehabilitative supports, can limit or avoid the need for drug withdrawal and cholecystectomy.