Smile attractiveness and the need for treatment of maxillary midline diastema with various widths are perceived differently between dentally trained and nondentally trained individuals of different sociodemographic backgrounds. This study aims to evaluate how laypersons, dental students, and dentists in Malaysia differ in their perceptions on smile attractiveness and treatment needs of maxillary midline diastema. A smiling photograph with well-aligned maxillary central incisors with proportionate width-to-height ratio and healthy gingival tissues was selected and digitally manipulated to create maxillary midline diastema with 0.5, 2.0, and 4.0 mm widths. The smile attractiveness and the perceived need for treatment of varying widths of maxillary midline diastemas were rated by laypersons, dental students, and dentists using the Likert scale via a single set of self-administered questionnaires. The impact of sociodemographic variables on aesthetic perception of different gap widths was tested using univariate analysis followed by a multiple linear regression model. A total of 158 laypersons, 118 dental students, and 138 dentists participated in this study. Both laypersons and dentists showed significantly higher mean aesthetic scores for 0.5 mm maxillary midline diastema, lower mean aesthetic scores, and hence higher mean treatment needs scores for 4.0 mm maxillary midline diastema as compared with dental students (p < 0.05). In general, female respondents perceived a gap width of up to 2.0 mm as aesthetically pleasing. Higher educational group and the Malay ethnicity had tolerance threshold of 0.5 mm gap width. The older group considered 4.0 mm gap width as aesthetically unpleasing. In conclusion, both laypersons and dentists accepted a 0.5 mm maxillary midline diastema as an attractive smile but considered 4.0 mm maxillary midline diastema as unpleasing smile which required treatment. Perceptions of laypersons and dentists were significantly different from dental students. Educational level, gender, ethnicity, and age were significantly associated with smile attractiveness of maxillary midline diastema at different investigated widths.