Analysis of Adherence in Subjects Undergoing Differin Gel, 0.1% Treatment of Moderate to Severe Acne Vulgaris

Inclusion Criteria: * Male or female Subjects of any race, aged 13 to 18 years inclusive, * Subjects with a diagnosis of moderate to severe Acne vulgaris, measured by lesion counts of a minimum of 15 and a maximum of 50 inflammatory lesions (papules and pustules) on the face, AND a minimum of 30 and a maximum of 125 total lesions. Subjects with nodules may participate in the study. * Female Subjects of childbearing potential must have a negative urine pregnancy test (UPT). * Female Subjects of childbearing potential must practice a highly effective method of contraception during the study * Subjects (and parent/guardian if Subject is under 18 years of age) must be willing and capable of following study instructions to the extent and degree required by the protocol; * Subjects able to follow study instructions and likely to complete all required visits; * Subjects/Representative signs the Informed Consent prior to any study procedures. Subjects under the age of 18 must have one parent or guardian read and sign the Informed Assent Form prior to receiving study treatment but the parent(s) or guardian is not required to attend the follow-up visits unless requested; * Subject must be willing to be photographed and sign a release form allowing photographs to be used. Exclusion Criteria: * Female Subjects who are pregnant, nursing or planning a pregnancy during the study, * Subjects with a condition or who are in a situation which, in the Investigator's opinion, may put the Subject at risk, may confound the study results, or may interfere with the Subject's participation in the study, * Subjects with known allergy to one of the components of the test products, * Subjects who have participated in another investigational drug or device research study within 30 days of enrolment, Subjects with acne conglobata, acne fulminans, secondary acne (chloracne, drug-induced acne, etc.), or or severe acne requiring more than topical treatment (e.g. oral isotretinoin); * Subjects with a beard or other facial hair that might interfere with study assessments; * Subjects with underlying diseases or other dermatological conditions that require the use of interfering topical or systemic therapy such as, but not limited to, atopic dermatitis, perioral dermatitis or rosacea; * Subjects who are at risk in terms of precautions, warnings, and contra-indication (see package insert for Differin Gel, 0.1%); * Subjects who foresee intensive UV exposure during the study (mountain sports, UV radiation, sunbathing, etc.); * Subjects with a known history of drug and/or alcohol abuse.