Android activity as dialog, but without a title bar

Try doing requestWindowFeature(Window.FEATURE_NO_TITLE); in onCreate. It'll need to be done immediately after calling super.onCreate and just before setContentView.

For those who are using AppCompatActivity, above answers may not work.

Try this

supportRequestWindowFeature(Window.FEATURE_NO_TITLE);

immediately before setContentView(R.layout.MyDialogActivity);

You can define your own theme:

<style name="NoTitleDialog" parent="@android:style/Theme.Dialog">
    <item name="android:windowNoTitle">true</item>
</style>

(Tip of the hat to @Rehan) If you're using the compatibility library, you should pick an AppCompat parent theme and leave off the android: prefix. For example:

<style name="NoTitleDialog" parent="@style/Theme.AppCompat.Dialog">
    <item name="windowNoTitle">true</item>
</style>